Honestly, Assassin's Creed 2 looks like the most fun game out of anything I saw at E3. It's gameplay demo wasn't hyped much, but man did it look ever so sweet. Ubisoft drastically improved on the original with a better setting and much, much better missions, while avoiding gimmicks. I just hope it's longer than the first was.
The only game that I'm looking forward to buy is Bioshock 2. Not too terribly impressed so far, but I'll give it a chance since the first one's story was so amazing. Most of the other impressive games at E3 I just don't own the system for, like God of War III (Loved the first two) and Heavy Rain (Bought its predecessor Indigo Prophecy and keep it for laughs). Oh Well. :|