Actually, Yeah to all of the above
The IGN review states what basically all of them say so far about the game...
IGN: Crysis Warhead Review
According to the review:
The Singleplayer is much more action packed and is even more open ended than the last with many fights all going on at the same time that often converge, and with less downtime between battles. There are several new weapons to use as well as new vehicles.
The AI has been overhauled and the enemies don't just stand around like retards any more. Alien AI are alot more aggressive and pop in and out of cover.
The old MP has been replaced with more action packed and less confusing game modes. There is a new mode called "Crysis Wars" which ships with the game as a taste of what Crytek will apparently release more content for later in patches. It's basically a Battlefield-style arena with lots of vehicles and places to go.
The graphics have actually improved over the last Crysis, and run [apparently] up to 30% faster on current hardware. Textures are sharper, explosions have a major FX boost, and the lighting has been optimized and is more balanced.
AND... it's only 30 bucks.
That's basically a paraphrase of the IGN article. I dunno guys, I was skeptical too, but it seems they may have a winner here.
FH Off Topic 
Crysis Warhead... 
Linear Mode
