Okay, here's the basics...Enter the Matrix is being developed in a proprietary engine, no liscensing is occuring. We all know this can either be a blessing or a curse, we'll have to wait and see.
You do not play as Neo, or as any of the movie characters. A seperate set of characters, and a parallel storyline has been developed. It allows the game to move on its own, and not rely to heavily on events from either the original movie or the sequels. However, it is said that it will cross paths with the sequels' storylines, and help explain some of the backstory that isn't developed too heavily in the movie.
The ability to slow down time and perform stunts and the like is provided by a recharging commodity called Focus (sounds a bit like using the force in one of the Jedi Knight games).
According to one of the devs, using stealth in the game will acheive nothing. It's intended to give all that Matrix action we've been waiting for.
"You'll likely also benefit from a meaty PC, as it powers a physics engine that allows your bullets (and other actions) to knock over tables, blow out ceiling tiles, and otherwise trash every square inch of the fighting space. I saw this aspect of the game in action, and it was truly stunning, perfectly capturing the chaos and destruction of the movies' monumental action sequences."
w00t

! Can anyone say "Lobby Shootout?"
Other than that, there's a sad fact that it will be singleplayer-only...of course, how could you handle bullet time in a game like that without it affecting everyone? Uh...weird.
The detail they've gone into in developing this has been truly astounding, and I won't go into it here. Rest assured we're looking at an excellent game in the future.