For me - totally Skyrim. I had never played a Elder Scroll game, nor a completely open world game (they way that it is.) I still fire it up from time to time years later.
Another one would be Alan Wake - never thought I would go back, play, and collect everything.
Runner up would be PacMan (Championship DX). I enjoyed the arcade, but was never very good - nor cared about being good. But this game is addictive!







