Just a simple question, what games you love to return to and replay? Maybe it's because they are your favorites, or it's sort of a comfort for you to play a lot. It can be once a year, once every few years, maybe more than once a year if you simply must do so.
For me, I must replay most of The Legend of Zelda games once a year, because it's my favorite series, and I find them so re-playable. Same goes for the main series Pokemon games, since I can use different teams, make up challenges, etc. There are others, but those two are top choices of mine.