After having played the demo some 10+ times, here are a few things I noticed:
1. Enemies can't knock you out of your charge stance as well as the first game. You're vulnerable initially, the same as the first game. However, once you see the blue aura surrounding your weapon (before you hit level 1 charge), the only moves that can knock you out of the charge stance are clearing moves that knock Ryu to the ground (typically combo finishers) or throws. However...
2. I'd say on the whole UTs are much less effective than in the first. Most are long combo strings focusing on a single enemy, with Ryu constantly moving foward or launching himself into the air, pushing the enemy you're UTing away from all the others. You'll be getting one or two kills most of the time, except with the scythe. The Eclipse Scythe's standard UT is by far the best. Even though it's linear, it has a near instant start-up (and finish), doesn't require contact to initiate, and is instant kill on everything it touches (of course these are one of the weaker enemies, can't say how it applies to later ones). Most of other UTs, save the Lunar's standard UT's flaming finish and its 360 UT's start up, are all flash and ineffective at crowd control.
3. It won't happen with all your moves, but there are a few combos involving Y presses you'll have trouble pulling off, as OTs tend to take priority in some cases. One example, the Dragon Sword's ->XX->YY->Y. Assuming second hit tends to knock off limbs, and unless you start attacking another enemy, the first Y press will most likely going into an OT.
4. Loss of a second limb is instant kill. You can still kill enemy and leave them with three limbs intact. It seems nearly impossible to kill an enemy and leave all limbs intact.
5. In the first game, you could hold block to prevent pick-up of nearby essence. While you can do this in combat in NGII, once combat ends you'll absorb all nearby essence orbs, regardless of whether you're holding block or not.
6. There's no limit to how much non-regenerative health you can have, I've managed to get it below one-tenth of the original health amount. With careful play, you could probably get it even lower.
7. Enemies are relentless and will chases down across multiple areas, even beyond the areas they spawn. Pursuing enemies, however, will disappear when you reach set fight areas (the ones that block off until all enemies are killed). In some cases, new enemies won't spawn when you reach new areas, but I did manage to have some 13 ninjas in one area. There was noticeable slowdown when doing so.
8. Flying Swallow is very gimp. In the last game (Black at least) a close-range Flying Swallow would be an instant kill on weaker enemies. Now it usually takes the full triple Flying Swallow to get the same effect in II, and the triple one is fairly inaccurate. This of course being a very good thing, though the FS is still quite abusable (this is the easiest difficulty level however).
9. I'll have to play Black to confirm, but it seems like the splash damage radius of the Izuna Drop is smaller as well. Not too sure about this one. Regardless, the splash radius is still pretty ineffective, essentially considering the larger swarms of enemies.
10. On the whole I'd say enemies are more resilient, but it also makes me wonder about the weapon power. In the last game, upgrading weapons added new moves as well as increasing weapon power. I suspect now that weapon power is constant, most likely for balance reasons, though obviously you'll get access to more powerful combos with upgrades. Can't confirm this yet though.