My top two would have to go to:
Final Fantasy IV. Still my favorite game ever. I replay it once every year or two these days but it used to be even more frequent than that.
Ninja Gaiden. The original, for the NES. I can beat it in about 12 minutes. My husband commented that if I were ever an Omeganaut and Ninja Gaiden were the final round, I would win.
But there are several honorable mentions:
Chrono Trigger, Cave Story, Super Metroid, Megaman 3, Heroes of Might & Magic 3, Forbidden Island/Desert…um…
I have a feeling Tales of Symphonia and Theatrythm: Curtain Call might both make this list, but I just played Symphonia for the first time last year so is it fair to put it on this list yet? (granted I am on my third playthrough of it now.) and Theatrythm also just came out last year so it’s kinda new to be “replayed” especially since I’m still unlocking achievements in it. Ask me again in five years.