Upon his death in 1973, J.R.R. Tolkien left behind a vast collection of writings about Middle-earth. His third son and literary executor, Christopher, assembled some of these into The Silmarillion, published in 1977, but the question about what to do with the other reams of material was unclear. Aware that fans of Middle-earth would be eager for more material, even unfinished or existing only in rough drafts, he assembled Unfinished Tales and published it in 1980. Its success inspired him to proceed with the far more ambitious, twelve-volume History of Middle-earth project.
Unfinished Tales occupies an awkward place in the Tolkien canon. Unlike the History series, which consists of almost exclusively non-canon material (early drafts and rough notes of material that was eventually finalised and published), the material in Unfinished Tales was specifically written by Tolkien to flesh out other parts of his mythos that were not explored in the books themselves. In particular, the writings include a series of essays which were designed to answer a wide number of issues brought up by readers of The Lord of the Rings and The Hobbit in correspondence. Some of these essays were written very late in Tolkien's life and represent his last - and often only - word on subjects such as the origins of Gandalf and his fellow wizards, the backstory of Galadriel and the history of Numenor during the Second Age. As a result some fans hold Unfinished Tales to be the fourth Middle-earth book, only marginally less important than The Hobbit, The Lord of the Rings and The Silmarillion. Others choose to disregard it as anything more than a curiosity, since as Christopher Tolkien himself notes it's unlikely J.R.R. would have permitted even the completed writings in the book to be published without more polish.
Unlike The Silmarillion, which was presented as a single narrative, Unfinished Tales is a collection of stories and fragments intermingled with Christopher Tolkien's editorial notes. These are kept to a minimum in some of the stories and essays, but in others are much more prevalent (something he apologises for, but regards as necessary in the case of works where his father was working on several drafts simultaneously, risking confusion to the reader). Christopher's notes are fascinating, well-written with a clear eye for detail and minimising confusion. He assumes the reader is already familiar with the Middle-earth mythos (since they're unlikely to be reading this book otherwise) and is able to delve into various topics in depth. Whilst he clearly loves and respects his father immensely, it is also amusing to detect the vague frustrations that creep into his notes, most notably when trying to fathom why Tolkien abandoned particular narratives at key points (feelings the reader may share as the book unfolds).
The first story is 'Of Tuor and His Coming to Gondolin'. The story of Tuor's arrival in Gondolin and the events leading to the fall of that city in the War of the Jewels was the first story Tolkien ever wrote set in Middle-earth, and is still one of his most memorable narratives. However, the version in Unfinished Tales was written much later, in 1951 (the much more complete original can be found in The History series), featuring a more conventional prose style than the archaic original. It's stirring, epic stuff, featuring some great imagery as Tuor is confronted by the Vala Ulmo, Lord of Waters, and has a great destiny laid before him. The story proceeds with power and momentum until it abruptly halts just as Tuor reaches Gondolin itself. Even with the earlier version available and a much more compressed account of events readable in The Silmarillion, this is still a frustrating moment.
The second story is 'The Tale of the Children of Hurin', a much longer story (almost a hundred pages, taking up a quarter of the book) featuring the adventures of the doomed, tragic Turin. Unlike the story of Tuor, this tale is more or less complete, though somewhat complex due to competing drafts and different versions existing. Many years later Christopher used this material (along with some other, later unearthed manuscripts) to form the basis of The Children of Hurin, so if you already have that book be aware that you will find much of this material familiar. But still, it's a powerful story, the darkest thing Tolkien wrote set in Middle-earth, featuring lust, incest (though unwitting), war and the 'hero' bringing death and ruin to all those around him.
The next section of the book moves into the Second Age of Middle-earth, which Tolkien left somewhat vague and under-developed compared to the First Age (covered in The Silmarillion) and the Third (the setting for The Hobbit and Lord of the Rings). We start off with 'A Description of the Island of Numenor'. For fans of worldbuilding, Tolkien's description of the island empire and the accompanying map will be fascinating. However, it's the following story, 'Aldarion and Erendis', which is more intriguing. It depicts the marriage of the noble lady Erendis to Aldarion, later King of Numenor, and touches on larger aspects (such as Aldarion's re-opening of relations between Numenor and the elves of Middle-earth), but for the most part it's a strong character piece. For those who claim Tolkien is overly-romantic, this account of a failing relationship due to outside pressures (Aldarion's lengthy absences from home) is surprisingly realistic. The story breaks off towards the end, although this is more of a relationship study than a tense narrative, so is less grievous a loss than some of the other texts in the book.
Tolkien follows this up with an account of the Kings of Numenor and the major events of their reigns. This is again primarily of interest to worldbuilders, but Tolkien manages to put in some great details and elements that could have been mined to produce further stories, but sadly it was not to be. This is then succeeded by an account of the history of Galadriel and Celeborn, something that Lord of the Rings fans will be more interested in, but frustratingly is also the most 'unfinished' of all the works in the book. Tolkien conceived of several competing, but radically different possibilities for the couple's backstory and reached no firm conclusions before his death, leaving several versions which are mutually contradictory. Christopher Tolkien suggests appreciating these contradictions as part of the literary effect of having a fictional history and mythology, which may be the best approach. Even in their differences, these versions reveal more fascinating information on Sauron's activities in the Second Age and characters briefly mentioned in Lord of the Rings, such as Celebrimbor, Nimrodel and Amroth.
The final sections of the book deals with the Third Age and consists mainly of finished essays and narratives, though in some cases with competing drafts which the editor takes pains to clarify. This section begins with an account of the Battle of the Gladden Fields (the engagement where Isildur lost the Ring), here revealed to be a much larger conflict than the brief skirmish suggested by Lord of the Rings and depicted as such in the films (by necessity, since Peter Jackson did not have the film rights to Unfinished Tales he could not use the account of the conflict here). He follows this up with the history of the Rohirrim, the development of the relationship between the Rohirrim and people of Gondor, and the founding of Rohan itself, again depicting worldbuilding information through a story (here the friendship of King Cirion of Gondor and Eorl, founder of Rohan).
This is followed by sections fleshing out The Lord of the Rings. 'The Quest of Erebor' explains how Gandalf came to join forces with Thorin and the dwarves and how he convinced them to recruit Bilbo Baggins to join their quest. This was actually a chapter from The Lord of the Rings, written as part of Tolkien's attempts to better-connect The Hobbit and the later work, but was wisely exorcised for killing the pace of the novel (it was supposed to be a discussion between Gandalf and Frodo between the victory over Sauron and the Scouring of the Shire, where it would have been ill-suited). However, as a stand-alone narrative it's a valuable - and enjoyable - asset in clarifying the relationship between the two books. This is followed up by 'The Hunt for the Ring', a detailed account of how the Ringwraiths set out in search of the Ring after losing track of Gollum (who had been captured by Aragorn). Though rather brief, this short piece does feature a memorable confrontation between Saruman and the Witch-King of Angmar. Rounding off this section is 'The Battles of the Fords of Isen', revealing in detail the battles fought by Rohan against Isengard on the Isen (alluded to but unseen in The Lord of the Rings). Again, it's not essential but does help flesh out a side-element of The Lord of the Rings.
Rounding off the book are three complete essays on three separate topics. The first expands on the Druedain or Woses, the wood-men who help the Rohirrim bypass Sauron's armies to reach the Pelennor Fields. Tolkien reveals in this essay that he was considering giving the Druedain a much bigger role in the backstory of Middle-earth, and even have them playing a role in The Silmarillion, but passed away before this idea could be fully fleshed-out. The second discusses the Istari, or the order of wizards that Gandalf, Radagast and Saruman belong to. We learn the names of the other two wizards who vanished into the east (Alatar and Pallando) and some interesting backstory emerges here. The third and final essay delves into the Palantiri, the magical seeing-stones which play a major role in The Lord of the Rings. This is atypical Tolkien, since normally he preferred to leave the magical elements of his world vague and mysterious, but here he delves into the capabilities of each palantir with the kind of magic system-building enthusiasm we now see with writers such as Brandon Sanderson.
Unfinished Tales (*****) is a fascinating book, representing a collection of writings by the most influential fantasist of all time extending over thirty years. Many of the individual stories and essays are excellent, certainly all are interesting and the only complaint that can be made is that several break off with no resolution. But then the book does tell you that on the cover, so it's hard to hold that against it. Unfinished Tales is available now, in numerous editions, in the UK and USA.