Crysis is pretty awesome. The AI is good to excellent, gunplay is great and the whole nanosuit thing adds tons to the open ended battle format. There are some less than brilliant bits, but the brunt of the game is pure class.
Honestly, at least judging by message board banter, the people blabbing the most about its incredible graphics and tech demo quality seem to be console fanboys of any sort using it as a neutral ace to diminish the value of whatever console exclusive that is currently being hyped. Most people I know who have played it call it a good game first, and tech demonstration a distant second.
By the way, I think calling it open world is pushing it. Far Cry 2, that's truly open. Crysis just gives you lots of room and plenty of paths to reach a point or complete an objective.