You could have reached a conclusion by playing the demo, or waiting for reviews from your friends or major publications. I read one review of crysis and it was quite clear to me that the AI was bad, and the gameplay was just an excuse to show off the graphics.
Demos are often non-existent or poorly representative of a final game. The Crysis demo, for example, isn't at all representative of the linearity and straight-forward action in the second half of the game. The Hitman: Blood Money demo isn't representative of the open-ended nature of the game as a whole. Demos can show the best or worst of a game and as such, can't be trusted to give an accurate and complete taste of the full product.
Similarly, reviews are unreliable. I read a number of Crysis reviews and none of them mentioned that the AI turns retarded when you play stealthy. That said, I don't think Crysis is a bad game. It just isn't worth paying full price for. When it hits the $20 range, I'll pick it up. I read a number of reviews of KotoR2 and none of them mentioned how blatantly unfinished the game was. Aside from that, you have the inherent subjectivity of reviews. I love the Gothic games but they got fairly average reviews from most reviewers. Were it not for piracy, I wouldn't have even bothered trying the games, nor would I have bought it them.
As a consumer and a gamer, it's in my best interests to make intelligent purchases and reward developers who have made good games. I'm not obligated to buy a game and hope it lives up to the hype.