Shattered has added a lot more polish, some story elements, some more interesting bosses and challenges, and removed the frustrating weapon breakdown element. It's under active development, whereas I think the vanilla game is now a dead fork.
While vanilla was promising, it always had that "school project" kind of vibe. Shattered, intead, is a full fledged, really polished game with active development.
Among the new features there are new sub-missions (with a new one in development right now), new enemies and bosses, a new playable character and re-balanced mechanics overall.
Stongly suggested, you can even find it on f-droid
I think I'll pick that up. When I quit playing years ago, it was because I felt like I had solved the game. Maybe my strategy wasn't optimal but it was as good as I could get it and I was purely relying on luck to get deeper. If shattered can add more depth then I'm down.