I guses the major event for today is, er, yesterday's release of Nexuiz 2.3 by Alientrap. Massive performance improvements due to an overhaul of the game engine, new maps, tweaked maps, tweaked weapons, sharper graphical effects, it sounds like a fairly extensive and very cool update to what must be one of the best deathmatch games around these days - and it's all Free Software. :-)
A russian list of open source games points out that Enemy Engaged: The Comanche Hokum is available under a GPL license, however it's just the engine and not the data which means you still have to buy the game to play it. It's a helicopter combat simulation and would be a really cool addition to open source combat simulations if they extended that coverage to the rest of the game (or at least made the data freeware). Otherwise I can't see the open sourcing of the game engine really making any kind of difference - it's not like it has massive exposure and a huge mod scene like the various games which iD choses to GPL the engines.
There are very few efforts to create single player FPS open source games. In fact, beyond Crystal Core, I'm not sure I can recall any noteworthy games.
Alientrap are working on a game, Zymotic, but I'm not sure it's going to be open source like Nexiuz although it will use the Nexuiz engine. There's some nice info on the storyline on that site but little else - other than a link to the curious 3D Element which seems to be a collection of game design tutorials. Note to self: investigate further.
Industri looked really promising a while back when Tenebrae (then Tenebrae 2) also looked promising, but both seemed to stall quite badly. There was an update yesterday to the Inudstri webiste though, and now it is being built on the Doom 3 engine but the screenshots seem to use a lot of Doom 3 models and Industri looks a lot less free than it used to - advertising for closed beta testers. I'm not sure it was ever open source though.
It requires a lot of effort to create the media (levels, characters, AI etc) to create a quality single player FPS game. I remember spending days, no, weeks designing single player levels for Duke Nukem 3D and requirements in terms of detail have escalated massively since then (and back then I was a kid with nothing to do except school and fun). The proximity of players to 3D models in FPS games means the detail has to be much higher than in other types of games; this genre does not lend itself well to the open source development model. I hope Crystal Core progress continues.
I got a request to reduce through-put on FG as apparently some readers can't keep up. And to think that I feet bad when I miss a day! Amusing. :-D