Well, for starters, here's your current lineup:
SF2: Ryu, Guile, M. Bison, Zangief
SF3: ChunLi, Yun, Alex, Urien
Darkstalkers: Demitri, Felicia, Jedah, Anakaris
SFA: Sakura, Karin, Guy, Rose
Red Earth: Leo, Hauzer, Mukuro, Null
New characters: Ingrid
Here's your different grooves/isms what have you. I think it's based on what character you pick.
SF2: No subsystems, but you do alot more damage, and apparently can delay a wakeup. I also think you get a super bar, ala Super SF2 Turbo.
Alpha: You get air blocking, custom combos, alpha counters, and weak supers.
SF3: you get the universal overheads, superjumps, quick stand, dashing, and of course, parries. CvS2 style parries though. You do get more then one super though, and 2 levels of meter.
Darkstalkers: ES and EX moves, air guard, chain combos, guard cancels, "moving wake up", and hitting knocked down opponents. They do less damage then other characters though.
Red Earth characters get guard cancels(Ultimate Counter) and super combos. They get gems by fighting, which can be used to level up or use supers. At the end of a round, though, they lose all levels. Levelling up makes them do more damage, and assumedly, take less. its done with both medium buttons.
Ingrid gets CvS2 style C-Groove, essentially. All grooves have throws done with the two weak attack buttons,
It's a team game, more or less. You choose which one of your characters you want to play as in each round, as my understanding. Super meters carry into the next round.
A few character notes-Alex's dash and normals are fast, but his specials are slow, and the darkstalkers characters absolutely murder him, since he can't use any of his mindgames against them.
Zangief does so much damage that his piledriver is almost Samurai Shodown-ish.
Jedah, Anakaris, and Demitri are prety dominant in this build of the game, able to use their subsystems well enough to pretty much destroy characters like a turtling Guile, or Rose.
Urien's Aegis Reflector got toned down.
I heard Ingrid plays alot like an SNK character, which could be interesting. I've heard one thing about this game-it's not boring. It's a fun game, and that's why I'm really looking forward to it. Supposedly it ends up playing like a cross between Alpha 3 and Guilty Gear. And I know I can't argue with that.