These are levels (or environmental art pieces), often WIP but not always, that I really liked -- and you should like them too.
Polycount Sidescroller Beat 'Em Up Contest
I'm kind of cheating here as all the entries are already finished, but seriously... Look at all these entries. Whoa. There's some really technically accomplished stuff here, like a wartorn research lab by Vincent "ParoXum" Mayeur, as well as a futuristic catwalk with a really strong color palette by Zach Fowler -- but my vote went to the stylized fishing pier scene by Nate "Skeptical Nate" Broach and Loren "Keen" Broach. I think non-photorealistic styles are often much more difficult to pull off, as I mentioned last month with the TF2 moon level, but this flat style really knocked it out of the park for me. Really great use of texture space, smart balance of details, and a very readable environment that would be really functional for an actual game (the floor and background are very distinctive, crucial for side scrollers).
Aladdin: The Fate of Agrabah by Eric Chadwick
Eric Chadwick did art direction for this 1996 PC game based on the Disney film. (Okay, so this is really really old. Whatever.) But classic design remains classic design; I could see this easily being an AAA iPhone game or Unity game today. So many technical constraints (limited texture memory, no lighting methods) but so many great solutions (the way they did the painted lighting, smart use of sprite imposters). Make sure you watch the flythrough, especially at the end -- including Mirror's Edge, so few games have the balls to use so much off-white in their environments... He's kinda right though. The city looks like Doritos.
Storm by "Falc"
I can't help my anti-Crysis bias; I'll probably never own the game, but there are all these custom levels I want to play. Argh. The great thing about Storm is how it solves the problem (of many Crysis mods always looking completely like Crysis) with heavy use of fog and really fine control of light -- it's not terribly special, but it's not easy either.
Untitled 12 Day TF2 Halloween Map by Cory "MrTwoVideoCards" De La Torre
He's probably not going to make his deadline, but I always like experiments like these because it's more about process than the product. How focused can you be? Is it possible to work consistently in Hammer without flying around aimlessly in the 3D view for 10 minutes, doing nothing? I mean, Valve probably isn't going to buy the level anytime soon, and it might get very little playtime (if any), but to finish anything is always an accomplishment.
(Stray thought: since Payload mode is based on Hunted from TFC, someone should make a custom payload cart modeled off the Pope-mobile so it's like you're actually escorting an VIP. PL_Vatican, anyone?)