I gave the Resident Evil 6 demo a try. Its split into 3 bits...
Leon's is ok. Its the very beginning of his scenario so 75% of the chapter is slow walking with nothing happening at all. The scenary and lighting are both great and its at least a lot more atmospheric than RE5 was.
Chris' Chapter is the opposite - its a very fast based section where you are fighting off against weird RE5 style enemies (they have guns which sucks, they are censored shots which is rather ammusing

). These enemies aren't as bad as they sound, as Capcom mentioned in the previews they do transform as the battles go on - some turn into monsters with wings, others arms mutate Krauser style and attack you that way. The cover system seems to suck, I can't figure out how it works exactly. Again, it looks great but it feels more like RE5 compared to Leon's chapter which feels more like old school RE games like 2 and 4.
Jake (Wesker Jr) is sorta a mix of both. His chapter involves facing off against a large enemy much like the first proper boss from Revalations (As in, he's bloody strong, has a huge health bar and has a bastard grab attack!). Not really sure what to make of that chapter yet. It was kinda fun and again it looked good.
There is one big problem in the game though - the camera angle when shooting. It zooms in considerably so the whole left or right side of the screen is taken up by the character and is bloody annoying in big battles (you could get easily blindsided). They need to zoom the camera out considerbly (it was perfect in RE4 so they should just go back to the way it was in that). If they don't fix it I can see it being a very annoying problem in the full game
The controls really needed more explanation. They are much better in this game than past games (they don't feel stiff or tanklike) but the game did a bad job of explaning how they worked (or more to the point, didn't explain at all)