For me the following games all showed glimpses of what 'next gen' could mean:
a) Uncharted - as mentioned already the little details, Nathan flinches, curses when you run out of ammo, his clothes get wet according to how deep he was submerged, the water as you went upriver (although I too found the barrels didn't work and detracted from the level - actually if you want to see an upriver level done right play Far Cry on PC for the river level)
b) Heavenly Sword - the big battles with, hang on, that looks like hundreds and hundreds of bad guys on the screen at the same time! The cutscenes were the best also.
c) R&C in terms of the animation, size of levels and just the crazy level of detail that was everywhere in every level
d) Assassin's Creed as you slip through (relatively) crowded streets then effortlessly ascend to look out over the entire city and its all there, no loading, no wait
e) Oblivion - when you first step from the sewer and really get to grasp the open world before you, and realise you could actually walk to the top of the misty blue mountain off on the horizon
Looking ahead - LBP. That to me has a chance of really defining next gen as something trully inovative rather than simply better visuals, etc. I'm almost dreading it coming out in case it doesn't live up to the promise.
Try to be reasonable... its easier than you think...
