LoK: Defiance is by far the best in the series. It retains all the good aspects of the old titles and throws in some new, well executed features as well. However, this game is not without some fatal problems which doom it to become a cult classic.
I have always loved the Legacy of Kain series, especially the last two Soul Reaver games which successfully mixed action and puzzle genres and almost movie quality storytelling and voice acting. Legacy of Kain: Defiance takes everything that was good in past games and takes it all up a notch. Defiance takes place chronologically after the events in Soul Reaver 1 and 2 in the mythical world of Nosgoth. While it is not necessary to have played previous entries in the series, you will be lost without the backstory, and it is highly recommended that anyone interesting in playing Defiance play Soul Reaver 1 and 2 first.
Graphics: The graphics in all of the recent games in this series have always been a high selling point. Crystal Dynamics puts some serious time into the graphical aspect of all the Legacy of Kain games and it shines through prominently in Defiance with excellent shadowing, lighting, and 3D design. Some of the environments are awe-inspiring later on in the game and while they may not all be critically detailed, they do the job more than adequately. The character models of both Kain and Raziel (the two main characters) are extremely well done, however, the enemy models (minus a few gorgeous bosses) are severely lacking in both detail and animations, yet this has always been a problem in this series.
Gameplay: The most impressive improvement in Defiance is definitely the gameplay. Crystal Dynamics completely revamped the combat system and now players can target enemies, use combos, collect new special moves, and use "Reaver Spells" to take out the respawning enemies throughout the game. Also improved is the number of enemies in the game. While there still isn't a great variety in enemies, there are much more to fight using your new combat skills. The camera angles are slightly improved over the Soul Reaver games, yet can still be a little fussy since most angles are fixed until you reach a certain point. Sometimes you will find your character obscured by walls and jumping can sometimes be frustrating, but overall the camera is less nauseating than before.
Sound: The soundtrack in Defiance left much to be desired. I have always felt the sound was the weakest aspect of this series and Defiance only reinforces that. The sound effects are decent, yet nothing to write home about. The only redeeming sound feature is the super-high quality voice acting done by the original Soul Reaver cast, which is executed just as well as previous games.
Controls: Controlling Kain and Raziel is much less of a chore in Defiance. The button layout is simple and easy to use, and the characters are responsive and move fairly fluidly. Since the camera is pretty much fixed, there will be an occasional control problem, but overall there is little to complain about besides some poorly chosen camera perspectives.
Fun Factor: I had a blast playing Defiance, much more so than the previous two Soul Reaver games. This is mostly because it wasn't so damn frustrating fighting with the camera at every turn and falling off ledges and having to run all the way around back to the starting point. The combat, although simple, is fun but will wear thin by the game's end. The difficulty level is also a harsh drop over Soul Reaver with very simple (repetitive) puzzles and enemies that really don't threaten killing you. The most fun, however, is had listening and watching the complex, twisting story unfold before your eyes and ears. The story is so enthralling you'll yearn for more and more. Playing the game will simply be an added bonus to discovering more story.
Overall: Defiance is a dream come true for fans of the series and truly feels like you're playing a well made piece of art. The story unfolds like a movie and the combat and puzzle solving keep you entertained between cutscenes. While it may not take too long to beat the game (20 hours max) and there is little reason to replay, Defiance is another great entry in the series which hopefully will continue onto the next generation systems.