@Innocent Portal series of games are among the best of the best games that I have played. If you like Portal, you would like The Talos Principle too, a mind bending FPS puzzler; and if you have the slightest of interest in a story that is basically the culmination of philosophy/theology/computer simulations/AI; you would absolutely fall in love with the game. Hellishly difficult rogue-like games (Spelunky, Nuclear Throne) have a special place in my heart. I also play a lot of indie games. I have a liking towards the games that force you to think and enable you to look at things in a different perspective; a couple of such games: Braid, The Swapper, Hotline Miami. I have been playing a lot of Hyper Light Drifter recently, great game. :)