I finally got around to playing the demo yesterday. To be honest, I wasn't expecting much but I really enjoyed it.
The graphics of this game absolutely blow me away, and this isn't even full graphics. My settings were at 1280x1024, no AA and all high setting apart from shadows, texture quality and objects quality, which were all medium. Walking through dense forest is truly amazing with lots of vegetation and amazing lighting effects. Floor textures look almost lifelike and the water is brilliant with some nice effects like bits of sea foam near the edge of rocks. Going for a swim in a game has never looked so nice!
The gameplay was really good and can be quite varied depending on what tactics and nano suit setting you decide to use.
The AI were pretty annoying, they seemed fairly dumb but with sometimes amazing senses. Like, for example, a boat that spotted me on one side of the map seemed to have super sight because even when I traveled to the other side of the map he knew exactly what bush I was hiding in from a mile away!
I was getting a steady 30-35fps on my system which consists of an C2D E6600, 8800GTS 320MB and 2GB RAM.
Overall I am very happy with Crysis and can't wait to get my hands on it.