Disclamer: Yes I am fully aware that the following two game do not have libre media, and that one of them will never have unless they get away from the copyrighted IP!
That said... the following two gems are really nice examples of what can be done with FOSS engines if some skilled artists work with them.. and they are free as in beer too :p
The first one has been mentioned before on FG, and is a Mod for the nice FOSS RTS Megaglest (Did we mention that one had a small new release too?). Annex: Conquer the World, doesn't seem to have it's one website yet (link goes to Moddb), but check out this awesome new video of that game (gives me a nice Starcraft vibe!):
Actually I don't know anything about the media license on this one, and it isn't released yet, but the closed development process makes me doubt we will have much luck in regards to the media (source must be GPL just as Glest), but hey... you never know!
The second one is as previously mentioned a bit tricky in regards to their media, but at least is is all publicly accessible in their SVN, and maybe you can ask if some parts of the media can be free-ed for other projects to use. Ok well which game am I talking about? Well ZEQ2lite ;)
Have a look at this video and I am sure you will recognize the copyrighted IP:
ZEQ2lite, has a longer history of different mods for Quake3, but this new version is based on a highly modified ioQuake3 version and is completely stand alone from Quake3. Not a big fan of the IP otherwise, but it looks nice and has cool effects :)
Oh and one quick last unrelated news... OpenWolf (a fork of Wolf:ET with Xreal renderer... long story) seems to be making some nice progress in updating this awesome (free as in beer but with FOSS code) multiplayer FPS classic, as you can follow here. And the original Xreal project seems to be somewhat alive too and a release is promised soon... looks like some healthy competition is going on there ;)