^^^Do you use the sticks or are you a button pusher?
If you use the sticks, like the game was intended to be played, you wont be disappointed. However if you're a button pusher it will probably suck at first because online play will not allow buttons, but from what I gathered single play will still allow it.
The new engine they added is for the actual physics of the game. This has me the most excited because it adds soooo much realism to the game. This means that arms can get tangled, bodies/arms/fists clash, etc. Not like on previous games where arms would go through arms, or your fist might go through there face or body. This is the dopest part of the new game, imo. Punches can now glance off your opponent, whereas before every punch landed was the same. Plus, this new engine allows for inside fighting, another huge plus and again adds to the realism. You can see in the gameplay video I posted, James Toney resting his head on Frazier's body, and Frazier's arms were kind of pushing toney's head downwards. Thats fuckin dope as hell because thats the physics engine at work and their body parts reacting to the events occurring, so it's not as robitic or predictable movements like before.
One thing I heard a game developer discuss was fighting with George Formeman. He said he loves how real it is because you can push off your opponent while their inside and nail him with a hook or a jab as he's traveling backwards, just like Foreman did in real life. Again, this is all due to the new physics engine.
It's not going to be perfect, but from what I've read and seen, it will be the most realistic boxing game to date.