It depends on the game.

RPGs I really like I'll play through again every couple of years (or, sometimes, I'll replay them three or four times back to back then never touch them again), but, for the most part, I don't replay RPGs. When I do, I tend to do challenge runs of them, such as a white wizard run of FF1, low level natural magic FF6 game, or random characters in Romancing SaGa 3.

That said, platformers and action games I enjoy I tend to replay fairly often. Pit-Pot, Legend of the Kage, 8-Bit Sonic 1, Shatterhand, 16-bit Sonic 2, Mega Man 1, 4, X2, and Rosenkreuzstilette, in particular, come to mind as games I replay a lot.