These days playing mainstream games to escape is more like just being embroiled into the modern world even more - No imagination, no creativiity, no fun at all.
jeffkiwi: ya this is true, I miss crazy weird games like Vigilante 8 on N64 and Chameleon Twist or whatever it was called.
If I ever sort out my life then I'd be interested in learning Open GL, to do 3d stuff (but without shaders). Seems like many games are made with Unreal or Unity but if I went back to basics I could make some cool time-killer games for free and release the source. Plus, it'd all work on Linux, and if it didn't work on Linux, it wouldn't need to be refunded because it'd be free :D
There are several game engines out there, but the two huge ones right now are Unreal and Unity. If you're worried about losing you math skills coding for one of these engines --don't. They do the heavy lifting, you still have to make things move the way you want them to do so.
I ended up going with learning Unity; it has a large community, tons of developer-oriented assets and has one of the best cross-platform spreads (unless you go with a Web-based engine). But I can only speak of those pros since it's the only one with which I have experience.
If you want to go open source, sign up on Github (BTW, they're owned by Microsoft now), but many other people have put up open source Unity projects.
Word of advice: sort out your life --I'd like to see what time-killer games you create.