i'm not excited about the possibility that it'll be a great game, but moreso that it'll tie into the movie very tightly. As cubist said, the main characters are Niobe and Ghost. The cool thing is that, as you're watching the movie, and a the camera shifts from a scene with those two, the game will pick up where the movie left off, with you in control of Niobe or Ghost. The brothers are writing the script for the game with the movies; it's essentially all one big script. So the actors may be filming the game one day, then the movie(s) the next.
From IGN's impressions, which are now a couple months old, it seems promising. It seems that in the version they played rewarded button mashing a lot in terms of fighting. The same kick combination, for instance, would render different, seemingly random results. i'd assume that the controls are very context-sensitive; so the same kick combination near a wall may involve your character springing off the wall to deliver a kick. They commented on other on other parts of the game (driving, ), which were overall positive, yet i have the feeling that after the first few times you figure how to do all the "classic" Matrix stunts, it'll get tired.
i don't doubt that Shiny can't deliver a solid Matrix game, but i do doubt that they can do it on all three systems while meeting the launch date, which is very important since the game ties in with the movies so intricately. The brothers' involvement, in my opinion, means very little to absolutely nothing in terms of how the game will play, or even look, only how well it'll tie into the movie's storylines. But if the game manages to keep the same ambiguity and mystique as the movie, it'll likely be a keeper for me.