It's not an fps but if you're looking for a free 'good' quality game, you might want to check out
this.
The game is called Lunia, it's an action MMORPG. No, don't stop reading just yet

Anyone ever played secrets of mana on the snes? Well, this game is kinda like that, only in MMO style.
Wait, a video says more then words:
[youtube]http://www.youtube.com/watch?v=7LaWEE2dblw[/youtube]
Basically, it's all realtime, it requires timing, skill and brains.
You play through episodes, all cut down in multiple stages (maps) that you need to complete.
The story is so so, evil dark lord blablabla, it's interesting enough to keep your attention but it's nothing big.
I'm having a hard time trying to explain it, just watch the vid and you'll know wether you could like it or not.
ps: The community sucks there, so it would be nice to talk to some players who know more then the following words: Idiot, noob, lol, etc (no, this usually wasn't aimed at me

).