Definitely somewhere between COD2 and Ghost Recon Advanced Warfighter. COD2 was the initial wow factor in graphics, same for Kameo whenever you went out into the badlands where an entire war between elves and orcs raged on. But Ghost Recon was the first game that convinced me that the actual gameplay features were beyond last gen. This is particularly true when considering the multiplayer and co-op terrorist hunts with Drone participation. It was the details and the drones that put it over the top.
"because 'Clerks' is NINJA in itself." - Ninja Mask lessons by Vern Reid (http://houseofninja.com/tutorial.php)
Gears of War for most people, I would assume. That, or playing the 360 version of a PS2 title, like Marvel: Ultimate Alliance or Superman Returns. Awful as that game was, it was pretty cool to see Superman's cape actually flowing in the wind instead of the piece of cardboard they used on the PS2.