Unvanquished is a fast-paced, futuristic FPS with RTS elements, pitting technologically advanced humans against hordes of highly adaptable aliens. The player can choose from either team, providing a fresh gameplay experience on both sides of the conflict. The game is under highly active development, with a new alpha release being made at the beginning of each month.
Unvanquished is the premiere successor to Tremulous, and is ambitious in its goals as well as excelling in artistic quality. While their work on making it multi-OS accessible is incomplete, this does not provide valid ground for any demerit. It's incomplete, and therefore cannot be judged on said incompleteness. The rest of their work is beyond fantastic.
One of the most promising Open Source projects I have worked with. The fast-paced yet tactical gameplay just doesn't get boring and will offer a lot to competitive players who love speed but hate shallow gameplay. Graphically Unvanquished is certainly heading for a place among the best looking FOSS games.
Good fun, nicely balanced, very original. Development is fast and updates are released frequently.
The graphics are nice (some great lighting!) but some areas need some big improvements (some of the weapons are pretty fugly, for example).
Another point is that there aren't that many people online, but I'm sure this will change soon!