A few things I remember from the disk (I'd imagine some of this is already common knowledge):
1) both fps and melee/hand to hand combat, with the viewpoint switching to 3rd person for melee
2) you can have combo moves in melee, and string hits together
3) differnet characters with have different abilities (strong and slow, nimble and quick, etc) and be better at different kinds of fights
4) all the weapons are revamped. For instance, the shock looks more like a cross between the shock and the ltg, and you're able to "freeze" the secondary fire in mid air, place several of them around, then combo them all at once. The Ripjack makes an appearance
5) you spawn with dual pistols, and the pistol types are specific to the species. I don't remember the species types, but one had dual "rivot guns" and I think I saw one with the pistols from Unreal 2.
6) They said something along the line of having to choose one type of mechanical weapon (rox, flak, etc) and one type of energy weapon (shock, ltg, etc) before you start a match.
7) The goo has changed in that the little puddles from the primary are ambient, in other words, they don't just lie around, but will actually chase you
8) there's a kind of assisted "lock on." It's not a lock and shoot type thing, but rather, it points you in the general direction, and you have to still aim. This is to counter the lack of control that plegues fps on consoles. Melee mode, though, is 100% lock on, so that you just have to concentrate on timing the hits and such.
9) There's a little bit of Mortal Combat flavor to the game in the melee fights
10) the maps and graphis look quite good
11) it appears that this was taking place at some sort of sneak peek thing. Someone was standing up and talking through the clips to an appearant audience, and he kept hinting that they were about to try the game out
12) in melee, you are given a shield to counter enemy fire. It's looks kinda like the effect from the sheild gun in 2k4, but it reflects fire and bounces it back.
I'll post more later if I think of more. Remember, I'm doing this based on memory. Don't crucify me if I'm not entirely correct.