I just played through the demo as well, and I'm really enjoying it. I'm glad grenades are back, even if they're the more traditional kind instead of those disc grenades from ME1. It seems Bioware kept their word with the talents and skills as well since there's a lot more of both. It's a bit early to tell, but it doesn't look like we'll be able to max out Shepard before the end of playthrough 2 this time, thankfully. I like the tweaks they've made to health as well. They seem to be combining ME1 and ME2 this time around with a sort of "heart containers" system like in Resistance. It's a nice compromise between traditional health and the T-1000 regenerating health that's in every game ever nowadays.
I do wish they had brought back looting and standard XP (from enemy kills rather than scripted points in quests and some containers) though.
If the rest of the game is like what was shown in the demo, it's likely to be a good game. It's rekindled my interest in it, something which I lost after certain decisions like adding multiplayer. I actually hope I'll be eating my words about the multiplayer as well.
EDIT: Also, does anybody else really, REALLY want to be able to
Spoiler use that pistol Kirrahe had?