Bethesda's games, since they're all huge and sandbox and reward lengthy exploration. And in second place would probably be Dragon Age: Origins.

Games that are too short on the other hand... Modern Warfare 2's single player was woefully short, and although it's the only CoD game I own, I assume the others are all the same. Bioshock is pretty short from what i remember of it.

Other games seem to be more lengthy, although most of the JRPGs I've played still aren't the length I've come to expect from them. But then considering what most if not all JRPGs have been like during this console generation, they're not worth playing for a whole slew of reasons other than length.