Since I stopped playing School Idol Festival (see below), I have turned to the rather new game Fire Emblem Heroes to satisfy my "mobile gacha game with math to be done" urge.
I discovered XCOM in November 2015. I really enjoy the emergent storytelling it allows, with unique soldiers and permadeath.
A friend introduced me to School Idol Festival around April 2015. It was completely unlike the games I normally played, and that was why it initially intrigued me. I kept playing because I found a great sense of community from the game. I enjoyed making tools and crunching numbers for the game.