Dude, are you serious? Such a vague question. Probably my entire NES, SNES, and Genesis library. I would rather play Megaman 3 or Streets of Rage over 99.9% of the games released in the last decade anyday.
I'm in the video games club at my collage and I'm the outcast because all they play are the newest installments of Halo or Tekken. And I'm the youngest one there, too! Kids these days...
It may also be because I grew up with the NES, but IDK.
Oh, and the PSOne, N64, and Dreamcast were kickass too!