The Lord of the Rings, written between 1937 and 1949, was published in three volumes between 1954 and 1955. According to Tolkien it was not meant to be three separate books, however the size of the manuscript (original manuscript is estimated at 9,250 pages) dictated the form in which the publications would take. This is seen in the structure of each book, which many Harry Potter fans have used against it without realising that unlike the Potter series which was planned to be a seven-series book, the LOTR was not. Each Volume does not have a complete arch; it does not visibly rise and fall. This structure is however seen when all the three books are taken together.
Though these books had been in circulation for over forty-six years, it was not until the movie production that the name of Frodo, Bilbo, Sauron, Gandalf, and Gollum became household names and Tolkien became a worldwide phenomenon. Today, only a handful of individuals could be absolutely ignorant about The Lord of the Rings. At least, they might have heard of the name or watched the movie if not read the books. Basically, the story is about good and bad. The Dark Lord, Sauron, is rising from his first fall and gathering his army in his tower. However, what he needs the most is his ring - the One Ring that rules all the other rings. It was in this Ring that he invested all his power during his earlier rule over Middle Earth. The Ring has however fallen through different hands in its response to the master's call. Isildur came into the Ring after the defeat of the Dark Lord. During his return to his land, he was attacked and killed by Orcs. The Ring then fell to a Hobbit-like creature called Deagol who was eventually killed by his friend Smeagol, later Gollum, when he claimed that it was Deagol's gift to him on his birthday. After several years of being under the power of the Ring, Gollum was beaten to it by Bilbo Baggins during a riddling game. Bilbo used it mainly for his disappearing act on his birthdays. In Bilbo's 111th year and his nephew Frodo's 33rd, the Ring passed on willingly from the former to the latter. It was during this period that the Wizard, Gandalf the Grey, whom Bilbo had befriended on his first journey, discovered the truth of the lore of the Ring. The power of the Ring and the fear of using it for evil purposes and its near-indestructibility led to the formation of the Fellowship of the Ring during the Council of Elrond in Rivendell. This Fellowship, made up of a Wizard (Gandalf), an Elf (Legolas), a Dwarf (Gimli), four Hobbits (Frodo, Sam, Pippin, and Merry), and two men (Aragorn and Boromir) were charged with protecting the Ring bearer - Frodo - to Mount Doom of Mordor, where it was forged and where it can only be destroyed. Thus, the story is about the journey of this Fellowship as they struggle against the rise of the Dark Lord and his machinations.
Unlike most novels, it is difficult to pinpoint the protagonist. Every member of the Fellowship, including Boromir who fell under the Ring's power and died for it and Frodo's friends Merry, Pippin and Sam, did something not just useful to the realisation of its ultimate goal but also played significant roles. Besides, though Frodo was the Ring bearer - during the journey to Mordor, for there were several bearers in the life of the Ring, he was not the Lord of the Ring nor had power over it. The Lord of the Ring was the maker of the Ring - Sauron, and the only one over whom the Ring had no power was Tom Bombadil. Furthermore, Aragorn's role was more than just membership in the Fellowship. The whole story revolves around him, even more than Frodo. His role in the past, present, and future history of Middle Earth was what moved the story. And his strength, intelligence, and presence contributed immensely to the successful realisation of Fellowship's mission and the final destruction of the Dark Tower. Aragorn appeared as Strider, a ranger, who was weather-beaten and homeless. Yet, he was the Isildur's heir, of whom the prophecy is about. He bore the sword that was broken and he was the crownless who became king. For after the destruction of the Ring, Aragorn returned to take his rightful place as Elessar King of Arnor and Gondor. Gandalf himself played no mean role in the Fellowship, especially after he fell into the Mines of Moria and his encounter with the Balrog. Though he was tempted with power from both Sauron and Saruman, he stood firm and with his wisdom saw through smooth-talkers like Grima Wormtongue and Saruman and the madness of Denethor, steward of Gondor. In a way, Tolkien showed that collaboration and cooperation is the only way to defeat evil so that for the sake of the fellowship, an elf and a dwarf - who were mortal enemies - became friends.
The beauty of the LOTR lies in its creativity, the first of which any reader cannot but mention is the beautiful poems found scattered in the books. Right from Tom Bombadil's speeches to the songs sang in Rivendell and Gondor, Tolkien spent time on his creation. The musicality, the rhythmic movements of the poems is such a beauty. As an example,
Three Rings for the Elven-kings under the sky
Seven for the dwarf-lords in their halls of stone,
Nine for Mortal Men doomed to die,
One for the Dark Lord on his dark throne
In the Land of Mordor where the Shadows lie.
One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them
In the Land of Mordor where the shadows lie.
This three-volume novel is one of the most complete creation of a completely different universe I have read by any author. The other is Frank Herbert's Dune. It is the intellectualism of Tolkien that I appreciate the most. His creation of Middle Earth as an epoch in the natural metamorphosis of the earth, inhabited by different creatures - wizards, elves, hobbits, dwarves, orcs, and men, with its own geography and historical events made Tolkien appeal to a wider audience including those who might not even like the Fantasy genre to which his work is usually classified. However, the important aspect of his creations is the sheer number of languages the philologist professor, who had a full-time job as a university lecturer, created for the different speaking-people that inhabited Middle Earth. So detailed was Tolkien's creation that he provided variants of the same languages spoken by different tribes of the same group. It is believed that in all Tolkien created over twenty different languages, each with its own grammar and vocabulary. He has been quoted as saying:
What I think is a primary 'fact' about my work, that it is all of a piece, and fundamentally linguistic in inspiration. [...] It is not a 'hobby', in the sense of something quite different from one's work, taken up as a relief-outlet. The invention of languages is the foundation. The 'stories' were made rather to provide a world for the languages than the reverse. To me a name comes first and the story follows. I should have preferred to write in 'Elvish'. But, of course, such a work as The Lord of the Rings has been edited and only as much 'language' has been left in as I thought would be stomached by readers. [...] It is to me, anyway, largely an essay in 'linguistic aesthetic', as I sometimes say to people who ask me 'what is it all about'. [Source]
The question 'what is it all about?' has led people to speculate and attribute all manner of allegories to the LOTR. However, in the foreword to the second edition (published by Houghton Mifflin), the author stated that he prefers applicability to allegories.
I much prefer history, true or feigned, with its varied applicability to the thought and experience of readers. I think that many confuse applicability and allegory; but the one resides in the freedom of the reader, and the other in the purposed domination of the author. 
In its applicability, the LOTR is about the fight between good and evil. And it is in the casting of the good and evil and the representation of its characters that Tolkien's magnificent creation - a creation of such humongous literary value and luminosity - is much criticised. Some have read this set of novels as a racist book that depicted all evil as black and all good as white or fair. There were Black Riders (or the Nazguls or the Ringwraiths) - the servants of the Dark Lord; there was the Black Gate of Mordor, the entrance to the Dark Lord's domain; Sauron - the villain - was the Dark Lord; the Dark Lord's tower was the Dark Tower; and many others. The fighting Uruk-hai, the strong and huge but brainless easily fooled type of Orcs, were described as 'black', so too were the smaller ones who worked as trackers described as 'black-skinned'. Sauron, the Dark Lord, was served by black men of the Easterlings and Southrons. In fact there are several lines scattered in the books that the race critics of Tolkien could easily referenced. For instance, at Bree, when the Fellowship were nearly attacked by the Black Riders, Butterbur - owner of the pub - swore that
No black man shall pass my doors, while I can stand on my legs. 
The distinction between dark and fair, light and dark, was sharp in this novel. Galadriel of Lothlorien, and Arwen the daughter of Elrond, were described as the fairest and the most beautiful. In fact, it was as if one's character type hinged on one's skin colour. Even when Saruman the White completely became evil he chose multiple colours instead of remaining white. In addition to these obvious racial characterisation, there were also class discrimination. For instance, Hobbits though white-skinned were constantly overlooked in Middle-Earth. Similarly, the fighting Uruk-Hai discriminated against the common Orcs, referring to them as Snagga. There have also been counter-arguments against these accusations of racism against Tolkien. The discussion in this area is broadening.
These are, however, not the only criticism of Tolkien's seminal work. The LOTR has also been charged with having few female characters in any major roles and reducing them to the conventional role of women. In fact, the Fellowship of the Ring included no female though individuals such as Galadriel played some very important role, in their own way. In addition to being a bearer of one of the three Rings for the Elven-kings, her gifts to the fellowship saved them from harm, hunger, and death. Eowyn cared for her uncle, Theoden King of Rohan, when he was under the spell of Grima Wormtongue. She had to disguise herself as a male soldier to be able to fight along side her uncle and in the end killed a Nazgul, which was no mean an achievement. Arwen, the daughter of Elrond - Lord of Rivendell - was known for her beauty and her marriage to the brave Aragorn who became the King of Arnor and Gondor. Yet, scarcely any of the female characters in the LOTR was assigned the traditional female characters of witch, sorceress, temptress, and others.
Whether these references and characterisation were metaphorical or that the criticisms might have arisen from an age where events have led people to develop a more sensitive ear, any book as popular as this is likely to be such charged even if it were written in an age where these things were acceptable and would not have raised an eyebrow.
Aside these references, there were also some unique or curious biblical references one could make. First, Frodo Baggins - Bilbo Baggin's nephew - was 33 years, considered to be the age of coming of age for Hobbits. This was the age Jesus Christ said it was finished and died, according to theologians. On this same day that Frodo was 33, Bilbo was 111 years. Unless it is far fetched, does this not represent the trinity? Besides, the sum of the two ages - the uncle's and the nephew's - give 144 (or 12 dozen), which was the same as the number of people Bilbo invited to their birthday party. This number is considered gross by Hobbits, though it has Biblical reference. According to the Bible there are 144,000 people who are sealed (12,000 from each of the 12 tribes of Israel). Though this may not be significant, it is worth noting.
What is clear from reading the LOTR is that Tolkien was doing something much more than just storytelling; he was creating. First, the story was less suspenseful. Tolkien could have easily cranked up the suspense had he chosen to do so or had the story itself being his primary motive - something fans are now craving for especially when it comes down to the battle between fans (HP and LOTR). The sheer size of extra-reading material Tolkien added to the book detailing the histories of the various speaking peoples of Middle Earth, the chronology of events of Middle Earth, Family Trees, calendars, language used in the text, were of such intellectual merit that it moved the novel closer to history. In fact, these materials formed almost thirty percent of the Book III. Finally, even when the Ring was destroyed the story did not end there. It went on to tell of the scourging of the shire and the wiliness of Saruman as he made his way into the heart of the Shire and what happened to some of the major protagonists. It should also be added that for such an epic story, more pages could have been added. Tolkien agrees to this.
The significance The Lord of the Rings as a work of intellectual superiority that has spurned several books, researches, and studies cannot be eclipsed by the accusations and critiques charged against it. In a way these critiques are part of the intellectual study of the text. The work exudes quality and beauty. It breathes. To end, it is important to state that there are differences between the movie adaptations and the books. Tom Bombadil did not appear in the movie, though he was mentioned several times in the novel as someone very important and mysterious (even at the Council of Elrond, he was considered as an option when the solution to the Ring was discussed). This is not the only difference; there are others. Consequently, if one's aim is to enjoy Tolkien's creation in its entirety - the dialogue, poems, languages, historical events - one has to read the set and not relay on the movie. In addition to Tolkien's own material, other materials also exist that would help any Tolkien fan (or scholar) who wants to know more about the author's creations.