I'm moving away from proprietary apps and want to find open-source games on Android that are genuinely good, not just time-killers or kids' titles.

My criteria:

• Modern feel and polished experience — something that feels like a real game, not a tech demo

• Made for adults: deep gameplay, challenge, real progression (any genre welcome — strategy, roguelike, RPG, racing, puzzle...)

I trust actual players over AI-generated lists, so: what open-source game on Android gave you the best experience, and why?