These are WIP levels / env art that I liked, and most of them are hopefully close to release / are released. I command you to like them as well.
l4d_yama by Mark "the0rthopaedicsurgeon" Edwards
Four years in the making (?) and probably the most ambitious custom L4D campaign being made, surpassing even the impressive I Hate Mountains custom campaign. Whereas "I Hate..." was the work of three very handsome Europeans, l4d_yama is just a one-man effort, which is perhaps even more impressive. I've personally learned two important tricks from watching this map get made: (1) vignette the corners of a texture and add a subtle gradient to make it seem like one of those lightbox signs, as seen in the electric city section of this level, (2) use Propper once you've finalized level geometry to optimize everything, as Edwards did with all those signs in the alleys.
"Tron Scene" by Joshua "Vassago" Stubbles
I featured the concept art last time, but here's the final product. I chose the wireframe screenshot because I liked the way he did the giant blue laser writer tower things. Specifically, the furthest one in the back is actually a sprite imposter. Final Fantasy XIII did this a lot too, the ol' "real 3D tree close to you but fake 2D sprite away from you" trick -- and here I didn't even suspect it. Also pay attention to his gorgeous use of matte painting in the background... Mobile devices these days, e.g. iPads, seem to have a lot of texture memory but not as much polygon pushing power. Expect more matte painters to find work in mobile games and a shift towards higher production photorealism. (If / when Square Enix does a Final Fantasy game for iPad, it's going to make Infinity Blade look like scribbles.)
"Return to the City" revision by Bikerdude & Melan
I don't like the window frames in this shot (too thick; strange texture choice too; who makes windows out of stucco?) and the lighting is too flat (Doom 3's lack of ambient occlusion or GI forces Dark Mod mappers to rely on global ambient light settings)... but I want to call your attention to the walls: they're red. A flat, slightly textured red -- but still, a deep red. I would never make anything like this -- so colorful and domestic! -- it almost has no place in video games, especially if you consider how desaturated the two envs featured above are. Yet it works really well, I think. It isn't cartoony at all.
Rose Cottage by David "Saturnine" Tonkinson
It's a shame that the Thief mod community is so cut-off from the rest of the FPS community*, because they really put out some amazing work. Next to the Half-Life 1 engine upgrades done by the Russians, I'd say what Saturnine does with the Dark Engine is really extraordinary. Thief 2 isn't supposed to look this good! Of course, it also comes down to great art assets and placement: I like the balance of small details (stuff on table, engravings) with medium details (railing, curtains) with white space (the subtle wallpaper). It's not overwhelming.
* What's more strange is that many Thief modders regard level screenshots as "spoilers" -- well, how else can you promote anything?!
PS: the author now works for Arkane, I think, along with several other prominent Thief modders, on a rumored Arx Fatalis 2 (?)... Exciting!