I'm big on art style when it comes to games. Jet Set Radio still looks good to me because of its style, even though it's an early 6th gen game. I'm a sucker for the cartoony Jak and Daxter art style too. I also really liked the visuals on some other 6th gen games such as Metal Gear Solid 3: Snake Eater and GT4. The Soviet jungle/Groznyj Grad in MGS3 still holds up pretty well for me, and not just in the HD version of it.
Human contact, the final frontier.