Worthy games only available on Steam

[Agozer]

So I was browsing Steam a while ago and bought Alan Wake and all its extras for less than €4, and that got me thinking...

Need recommendations for great/good games that are only available on Steam (not on X360 or PS3), and are not necessarily huge AAA titles. I don't care much for western RPGs nor simulation games, so puzzle games, action games, shooters, adventure games and what have you are welcome.

[sweener2001]

Games I own that I enjoy:
Dungeons of Dredmor - A hilarious roguelike
Puzzle Agent 1 & 2 - Simple point and clicks with lots of puzzles
Titan Quest - an older Diablo clone, very fun
Machinarium - A tough but adorable point and click
Orcs Must Die 2 - co-op action tower defense, with a sense of humor
Defense Grid - a more classic tower defense game, may not jive with your no strategy games request

Games I own I want to get to:
Analogue: A hate story - interactive visual novel
Hard Reset - a very pretty but old-school style FPS

Games I own that aren't only on Steam worth mentioning:
The Walking Dead - loved this game, the story is incredible
Tomb Raider (2013) - I had a good time, even if they strayed from the series' roots
Spec Ops: The Line - I loved the campaign
Torchlight - another Diablo clone, but by ex-Blizzard North employees
Alan Wake - nothing new for you, I just need to remind myself

Games I don't own that I hear good things about:
FTL: a roguelike, IN SPACE
Recettear - A JRPG from a shopkeeper's perspective
CS:GO - the newest iteration of Counter-Strike
Torchlight II - now with co-op

With the summer sale coming up in about a month, you should be able to get a heck of a lot of those (if they interested you) for about the price of one new game. You said you didn't like WRPG's much, but I included the roguelikes as they don't necessarily fit that bill.

I recommend checking out the current humble weekly sale and HIB 8, as they both have some good stuff in there.
Humble Weekly is a lot of Telltale point and clicks, which includes the walking dead if you pay over the average. Dear Esther and Thomas was Alone in HIB 8 are well received, from what I hear.

[Agozer]

Thanks, I'll look into those. I already own The Walking Dead on the PS3, and it's indeed awesome.

[kode54]

Games I own that aren't only on Steam worth mentioning:
...
Tomb Raider (2013)

The retail copy from Origin comes as a Steamworks installer and product key, installs through Steam. I'm not sure about actual retail copies, though.

[sweener2001]

Yeah, all PC copies go through Steam; that category was meant more for multi-plat releases.

Dishonered should go on that list as well. Good fun.

[Gil_Hamilton]

Well, it's not only on Steam, but La Mulana is pretty sweet. Also Super Hexagon, which is my addiction.