Dwarf Fortress (PC/Mac)SimulationBay12 Games2006
"The Hardest Video Game Ever Created" is about right. That is what makes it great.
Defender's Quest: Valley of the Forgotten (Mac)Tower DefenseLevel Up Labs2012
A tower defense RPG. Two great tastes that taste great together.
Marvel Puzzle Quest (iOS)PuzzleD3Publisher2013
A game that has its ups and downs, but always manages to remain addictive.
Final Fantasy (iOS)RPGSquare Enix2010
One of those classics that I played long, long ago without actually finishing. It was alright.