Aside from all the free games from GOG or whatever, I have a handful of games on Steam that I purchased between 2013-2015 and have no idea why I got them in the first place. Borderlands 2 I bought in 2013, played for about 15 minutes, and then only recently picked up again. Mount & Blade I mentioned earlier post. I got some decent playtime out of Just Cause 2 but I have no idea why I got it in the first place.

Same for Fallout 3 and Fallout: New Vegas.