I quite liked Endless Sky (which is no surprise because I quite liked Escape Velocity). Last time I tried it, the storylines were far from finished, but it was a good time.
It's got that... "in progress" feel -- and probably always will.
I love how many people it has fiddling with the code and storyline.
I know it's not something that can realistically happen, but I'd love for all games to switch to open-source after a few years of being available commercially.
It's cool to see continuous development on Endless Sky. At times... wish some features and improvements would go faster, but hey... that's part of playing with a non-commercial product. It's just a casual train-set in my basement... tinker a bit, play a bit, it's just sort of fun to see both sides.