The PC version has better controls and (most importantly) it can be patched, so if you've got a good computer, get for the PC. If not, get it for the Xbox. Either way, get it.
Deus Ex: Invisible War is the sequel to the PC classic, and a welcome return to a dark, open-ended sci-fi world filled with conspiracies and moral ambiguities. The story starts when society is trying to rebuild itself following the catastrophic ending of DX1. You play as a biomodified anti-terrorist cadet who is forced out of the academy and into the real world. There are many rival factions trying to create a new world order, and all of them have one thing in common: they need you to help them accomplish their goals. The story is dark and complex, and delightfully lacking in pure good, pure evil, and happy endings. I'd recommend playing the first Deus Ex before tackling Invisible War. That way, you won't be really confused when the characters start whipping out names like "Helios", "MJ-12", and "UNATCO".
The gameplay in Deus Ex is nothing special. The game is more of an RPG than an FPS, so don't expect too many intense firefights (though there certainly are some). The fun comes in choosing your path. This is the videogame equivalent of a Choose-Your-Own Adventure book. You can kill a main character when the chance arises, and their death will be written into the story. There are even four possible endings, which is awesome.
Problems...Well, certain gameplay elements from DX1 have have been a bit simplified, but its not nearly as bad as certain reviewers make it out to be. Also, the combat and stealth are fun, but nothing special. You should also know that the game controls better on the PC.