I beg to differ. Go back and play Grim Fandango or Sam and Max and tell me they aren't still fun.

What we're seeing as emergent gameplay comes into the forefront is that it's becoming harder and harder to tell a cohesive story with a cinematic feel. Yes, there's something to be said for non-linear gameplay, but I feel both linear and non-linear games have a place in the future of entertainment.
Some people complain that certain games are "too scripted", but there's nothing wrong with scripted sequences if they help immerse you in an experience that's bigger than just your effects on the environment. Games like Medal of Honor, Call of Duty, and Half-Life 2 may not be revolutionary, but they're still fun. (Yes, I'm an FPS player primarily.)
This isn't to say there's not a place for San Andreas, which does a fair job of weaving free-form gameplay with a linear story progression.