Old school nintendo

As far as NES, I'm gonna have to go with Super Mario Bros 1 and 3. Maybe Megaman to, but I just recently started playing that, while I've been playing mario for quite awhile. There's a few more things I like on the SNES though like Mario Kart, Earthbound, and Super Mario World. I used the SNES a lot more then the NES so I can't say much more about the Original Nintendo.

I loved everything JodyLee mentioned above as well as Ninja Gaiden & Guantlet.