I think the only game series I definitely replay almost every year is the Metroid series. Lately, it's mostly been either Metroid, Metroid II, or Metroid Prime 1. In fact, I just beat the original Metroid about a week ago (I'm gearing up to write a review).
I think this time around, I'm going to play the Meroid series in the chronological order the series has established (Metroid, Metroid Prime trilogy, Metroid II, etc.). As you can probably tell, it's one of my most favorite game series in all my life of gaming (though I'm not a fan of Other M).