It's been a while since I last read a video game tie-in, but during the last couple of days I've had a chance to read Revan by Drew Karpyshyn.
It's set about three hundred years before The Old Republic, and like the title implies it focuses on Revan. He shares about equal page time with Lord Scourge however, a character featured in the Jedi knight class story, and there's a lot of background on the Sith Emperor as well. In a nutshell, the book tells the story of how all these characters end up in the positions they are in when you meet them in the game.
As I've mentioned multiple times before, I never played either of the KOTOR games, but even so it was quite obvious to me that the book relies heavily on the story foundation set by those two games. Apparently some KOTOR fans were rather unhappy with how this turned out, as their in-game experiences didn't match what has now been declared official canon. Supposedly some things were retconned as well. Personally I was unburdened by such emotional baggage however, and coming at it purely from a SWTOR perspective I was happy to be provided with some background for characters and events featured in the game.
The writing is fluid and fast-paced, and I soon had trouble putting the book down as I wanted to see where it was all going. Scourge in particular was a fascinating character to me: powerful and power-hungry, ambitious and paranoid. That's not to say that Revan himself was boring to read about, but relatively speaking I found Scourge to have the more interesting personality.
The book also ties in very tightly with the game without being cheesy. Seasoned players will recognise familiar locations here and there (such as the Nexus Room Cantina in Kaas City), and many of the fighting moves described during the combat sequences are reminiscent of actual in-game abilities. There's even a small reference to the player character.
Like any good tie-in should be (/cough), it's completely optional reading. Even if you've never heard of Revan before by the time you encounter his name in the game, everything relevant will be explained as you go along. However, if you'd like to know more about how he ends up where he does, or almost more importantly how the Emperor has ended up where he is, I can heartily recommend this book to fill in all the gaps.