When the original Halo came out I hadn't seen anything that impressed me particularly until about two weeks before it launched. Even then no single element of the game blew me away, but as a whole the experience stcuk with me in a way that games like Super Mario World, Street Fighter 2 and Super Mario 64 did. I think it was the neat little details, the amusing alien speak, co-op warthog sections, plasma grenades - everything just came together so well (library level not included in that statement of course).
With Halo 2 the expectations were that much higher and Bungie/Microsoft revealled more information prior to the launch. As with most sequels (films etc included) it was difficult to live upto the expections.
With Halo 3, however, there has been very little revealled regarding the the single player mode and I reckon there'll be loads of clever little surprises that wow players. Personally, I can't wait to find out.
Assassin's Creed, Halo 3, PGR4, Bioshock, Resident Evil 5, Mass Effect, Devil May Cry 4, Grand Theft Auto IV, Burnout Paradise, Super Mario Galaxy, Metal Gear Solid 4, NiGHTS, Heavenly Sword... with so many AAA titles on the way I don't know how anyone could be disappointed with this year's show. Still, some people are never satisfied.