TERRARIA
Terraria
Terraria is a sandbox action/adventure RPG.
The game features exploration, crafting, construction, and combat with a variety of creatures in a randomly generated world. It has similarities to Minecraft but it's in 2-D. I find this very addicting played it for 400++ hours. It also has multiplayer and mod support.
DWARF FORTRESS
Bay 12 Games: Dwarf Fortress
Dwarf Fortress is a rogue-like, part city-building FREEWARE video game set in a procedurally-generated universe in which the player takes control of a group of dwarves and attempts to construct a successful and wealthy mountainhome. The game is mostly presented in "extended ASCII" graphics. The gameplay is extremely deep and complex. It has mod support. If you wanna try the game, try the "lazy newb pack" mod.
GNOMORIA
Gnomoria
If you find Dwarf Fortress too hard to comprehend then I recommend it's milder, better looking younger brother, Gnomoria. Gnomoria is a sandbox village management game where you help lead a small group of gnomes. You can mine for resources, craft, build structures, etc.
FTL: Faster Than Light
FTL: Faster Than Light
FTL is a top down rogue-like space strategy sim. You control the crew of a single spacecraft. The games has one of the best replay values.
TO THE MOON
To the Moon
To the moon is more of a visual novel than a game. The game only lasts about 4 hours, but I'll confidently say that this is one of the best 4 hours of my 20-year gaming experience. This is the 2nd game that got me in tears (1st was Chrono Trigger). I'll rank the story and writing to be one of the best in the gaming industry (it won Gamespot's 2011 best story award) and it is complimented by amazing music. If you like games for their story, then I highly recommend this.