For my money, the original Crysis beats its sequel hands-down. Huge open spaces and massive bases (complete with enormous enemy numbers to match) can be countered with a variety of different suit powers and tactics. Seriously, no two games are ever quite the same, and the scope for new styles of play and desperate invention is staggering.
Oh, and the graphics are pretty good too. Considering that you'll get a physicl copy rather than a download, Bee.com's price is rather nice.