You Have to Win the Game is a very interesting platformer game that has just been released on Linux. It's interesting because it's so retro it emulates old CRT screens (you know those screens we had before flat-panels) so it feels like you're playing on an old PC.
If you haven't heard of Outcast before then you are either young or living under a rock, possibly both! Outcast was a revolutionary open-world action-adventure game back in the day. Outcast Reboot HD is promising Linux support at a hefty stretch goal.