I'm actually going to say action games. Things like Assassin's Creed, Resident Evil 5, etc. I think back to the PSOne and N64 and so many of those action games have been made null and void because of advancing technology. The beginnings of 3D were very cruel to action games and I can barely think of anything from that era that still hits as hard as it used to or hits hard at all.
Edit: I thought I'd mention also that I think SHMUPs, both the R-Type and Contra varieties age the least overall. Many of the oldest are still fantastic to play through, the genre has barely advanced at all after all these years and the newest ones are awesome to play for sticking close to conventions made 15-20 years ago. Puzzle games too. A good puzzle game does not age.
Tag: Became a freaking mod and a complete douche, coincidentally, at the same time.
