the 2900xt isn't all that powerful of a card. it certainly beats most of the other Radeon models. but in terms of being able to keep up with the demands of Crysis, i don't think the 2900 can handle it. system requirements lab recommends a Core 2 duo 2.2ghz or better, an 8800gts 640mb or better, and at least 2 gigs of RAM.
your AMD processor lags seriously behind most of the core 2 duos in terms of performance. and your 2900xt lags behind the GTS. i think your system can't handle the graphics well enough.
now don't get me wrong. you have a very nice system. all i'm suggesting is, it's not powerful enough. it could very easily pick apart just about any other game. just not crysis.
i guess the overall message is Crysis may have been too ambitious with not enough effort put in the right places. the graphics are phenomenal. and so were some of the intricate details like tripping on stuff, or shooting out tires and things like that. i think that's great. but it wasn't developed enough. it was as if they made a few cinematics, and decided to turn it into an FPS, and then slapped on some stupid story they thought up in 5 minutes.
the graphics are almost too intense for the average consumer. not everyone can afford a top of the line PC that can render such powerful graphics. and the game has to be enjoyable for a very broad number of people. and so far 90% of the people i've talked to were hardcore gamers with top of the line PCs, and almost all of them said it was terrible.