Played through Portal recently, which was fun, even though I always struggle with my sense of place in FPSs, as in real life. Some of the memes this game has spawned baffles me, though (companion cube? Really?).

So I went back to Half-Life 2. Can't say why I abandoned it all those months ago, just before entering the Citadel, but I finished it in no time, and played through Ep. 1 and 2 the following day.

As many other's, I found it inferior to the original in terms of level design and variety. The Strider battles were always fun and intense, but they don't convey the awe I got from killing the tentacles and pyros of the first game, enemies you had to defeat through manipulating the environment rather than restocking your rocket launcher from an inexhaustible ammo crate. And did the marines of the original have better AI than the Combine troops, or is that just glossy nostalgia?

But the atmosphere is above reproach, and the personalities of your companions every bit as believable as I was led to believe. I really didn't expect to care for Alyx as much as I did. I'm also looking forward to seeing how the story pans out, although I wouldn't be too surprised if Ep. 3 ends with some manner of cop out.

So now, with Ep. 3 and Black Mesa: Source nowhere on the horizon, and a month to go for Bioshock 2, I need an FPS fix.
But I'm particular; I care more about an immersive environment and atmosphere than gameplay, and I'd rather it be a fantastical setting. Played Halo, Far Cry and Crysis, and didn't care for any of them, and the undertones of the Modern Warfare games make me decidedly uncomfortable.

I have S.T.A.L.K.E.R., which I'll play after patching the fuck out of it, and I'm going to replay Republic Commando, but does anyone have other suggestions?

Thanks, in advance

EDIT: Not a graphic junkie either, so lost gems would be appreciated.