I loved GTA III and Vice City (but not VC Stories), Loved the scale and scope of San Andreas (but not the having to eat/date/dress crud that had begun to intrude) and like a lot of you, found GTA IV left me cold. The core game experience seemed to have drifted too far, and up itself.
The new trailer - though I hate that it's 'cut scene' material rather than simply in game footage (I hate cut scenes, just let me get on with the game ffs!) - seems to signal a return to the San Andreas' era gameplay rather than continue along the evolutionary path of GTA IV. Notice the introduction of things some rival games do well, like the grapple hook.
If I'm not forced to perform tedious repetitive drudgery like keeping irritating girlfriends happy or having to eat, maybe not having to retain territory (wasn't too bad in San Andreas, was just no fun Vice City Stories) then this slightly nostalgic looking GTA could be a real blast.