Paying close attention to the trailer it seems that the "ATB" gauge fills up when attacking, and that when filled allows characters to do personalized special attacks that probably aren't connected to the materia system.
People are already going on about the "limit breaks" used in the trailer, but if people paid attention they'd notice that non of these attacks are done when the limit bar is charged, but rather when the "ATB" gauge is charged.
This seems to indicate that the bar in front of the name is a combo-gauge of sorts that needs to be filled up in order to access special character attacks (perhaps even the other commands such as magic, or summon).
That would certainly be welcome as it would add a layer of personal difference to the characters apart from the limit breaks which the original game lacked, and which also serves to break up the melee combat so it does not devolve into a process of cookie-cutter button-mashing.
I'm really not feeling the design of Cloud though.
Biggs and Jessie look awesome, and whilst Cloud looks decent in motion when you can't make out the details, when he stands still he looks positively horrible.
That hair looks like the kind of cheap wig I expect from low-grade cos-players at gaming conventions.
Those spikes just don't translate well when you've decided to animate pretty much every single strand of hair on his head.
Also, what's up with his face - that last scene when he looks up - seriously creepy and freakish.
I'm indifferent to Barret. He needs to take off those sun-glasses though - Matrix grew out of fashion a decade ago.
So in short - I think the game-play looks okay. Nothing spectacular but not horrible either. I think the design and presentation is generally solid - but I can't stomach that Cloud. Fix his face and hair asap Nomura.