Yeah the demo is pretty cool I think... new "boss"/"unique" infected are kinda cool too.
The "spitter" or whatever (zombie meth addict?) is pretty cool since she can basically block you from going places, and even when you kill her she leaves some goop on the floor, so you can't go towards there right away for a bit.
The "charger" seemed like a mix of a hunter and tank (although not as strong as a tank... just in looks I guess). They should make the charger stronger though (more health)... he's always sooo easy to kill.
And IMO the jockey was just weird.

That laugh he does when he's walking (running?) around just creeps the hell out of me.
Also I thought the boomer bile thrown-weapon (same slot as pipe bomb and molotov) was a pretty neat idea.
I also like how there's slightly more variation in the weapons. Like not just one single pump shotgun, Uzi, pistol(s), M16, M21, M1014 (auto shotty), etc. Like for the pump shotgun, there's the normal black and wood one, but there's also a fancier chrome and black one that you find sometimes. And there's the silenced Mac-10, but there's also still the Uzi (although they're both basically the same). And even with the assault rifles, at least now there's two (so far). The burst firing SCAR-L and the full auto AK-47, etc etc. The melee weapons are also nice, that's a great idea.
BUT I think that they should tone down the damage of the melee weapons on normal/advanced, because unless you are playing Expert the melee weapons are way OP. Like, taking down a horde with a machete and not taking a single hit is sorta ehh.