You can only pick 2 games from steam to play for the rest of your life, what games are they?

I have a large library of steam games, but yet always come back to Garry mod and ravensfield. I keep coming back for the modded content and every other game is excellent, don't get me wrong. But a lot of big games like RD2 and watchdogs 2 just seem like such a long time investment. What 2 games do you infinitely come back to?