I do feel like this generation games like Assassin's Creed, Uncharted, Portal, Left 4 Dead, Borderlands and Super Mario Galaxy were genuinely new experiences and things that really could not have been done before.
Mario Galaxy could have been possible before, technically speaking. They used the polygon surface normals to figure out gravity instead of doing giant world calculations ... so that might have been potentially doable even on N64 ... though ... without enough polygons on the ground ... it wouldn't have worked well at all
Assassin's Creed that really wasn't possible from a technological standpoint. The way the parkour worked, the amount of context sensitivity required with the world and even the amount of animations. Not to mention the collision calculations.
Uncharted ... specifically 2 ... was absolutely not possible on earlier hardware. There is no way to create environments where the camera can seamlessly move from external to internal with no loading and actually having objects move in the world hierarchically was a really big deal too.
Obviously ... Crysis not remotely possible before ... but that really was all graphics ... it didn't inhibit the gameplay at all. These other games, these technological advancements are what made them possible. Crysis came out a few years earlier it was called Chrome.

I do agree that there just weren't enough games taking advantage of the advancements that were there to really make something new. Maybe Dead Rising too. But it really is a short list ... the big thing this gen was reviving the past.