I think the relaunch of Monkey Island on the iPhone proved that adventures are far from dead. Are they still mainstream? Maybe not, but I definitely see elements of adventures in modern games. Games like Fallout 3 and Bioshock rely heavily on storytelling. You could argue that some sandbox games like GTA San Andreas (haven't played IV, sorry) are technically adventure games or have adventure components. While I think…
Compare Bioshock to System Shock 2 though; Bioshock is extremely simplified in order to still be playable on point-n-grunt console platforms.