Crysis is a visually stunning game with thrilling game play, fun fights and good replay value.
Talking about characters, one memorable character is the nano-suite. It adds a certain value to the game play. It allows you to approach any given situation from multiple angles. From stealth to rambo anything is possible. Huge area also adds to the variety of approaches. This is what makes the replay value of this game. And you should try all, they are all fun. Destruction does not really add to the game play, but it is fun too.
AI is superb than in any modern game. Yes! I mean it. There are some problems, but still the best. They react to nearby situations, attack in groups, run, hide, cover... they are good. AI and adaptive difficulty make the fights (they are not always fire fights!) fun and always keeps up the pressure.
The story is good and the story-telling is good. It's not like kill some bad guys and I'll tell you some more... In my opinion, story and game play don't go well together. Either you can tell a great story or you can have a thrilling gameplay. And with the awesome visual beauty Crysis have, it would have been a disaster if it went on with story-telling.
HL series was holding the benchmarks for both game-universe and visual beauty, now they have only game-universe :). Crysis is, without doubt, a benchmark for modern day shooters. It's been holding the title for almost 4 years now, and sure will hold it for some more.