Great Steam Games?

There aren't actually any games on Steam except the ones Pewdiepie has played.

Well Let's see here, from my own list.

Little Inferno
Metro 2033
Left 4 Dead 2(honestly all the campaigns from the first have been ported to the second, so no reason to get the first now)
The Elder Scrolls Series, at least from Morrowind to Skyrim
DLC Quest
Sribblenauts Unlimited
Surgeon SImulator 2013
Crazy Machines 2: Elements
Quantum Conundrom
The Orange Box(Which now includes All of Halfe Life 2 along with Portal)
Portal 2
Dead Island
Bully
Just Cause 2
Insanely Twisted Shadow Planet
The entire Deus Ex series
Doom 3
the Paintkiller Franchise

I would have listed Audiosurf and Beat Hazard, but, you could easily run into copyright issues there.

the game too the moon i heard was good i think pewdiepie did that one as well.

Any of the L4D games or G-mod would be pretty fun.

FEZ is an awesome indie game, and it's only ten bucks. It's still fairly new, so there will probably be some dlc for it soon.

not sure if it counts seems it's not officially on steam yet, although it runs on steam and uses the source sdk 2007 engine, Black Mesa Source, possibly one of the greatest game remakes ever for one of the greatest games ever

I like Killing Floor, Team Fortress 2, Grand Theft Auto and.... Well, these are my personal favorites.

My favorite are the Total war games like Medieval 2, Empire, Shogun 2 and I so badly want to buy the new Rome 2 game.
I also like Red Orchestra 2, Company of Heroes(all of them), Killing Floor, Poker Night(1st and 2nd), Max Payne(only the 1st and 2nd because in my opinion the 3rd one is not a Max Payne game at all).
These all are great steam games, so...
Go nuts!

Best one ever would probably be GMOD, Garry's Mod. Only like 10 bucks on steam, and it has thousands of possibilities for games and maps, so it's essentially 10 bucks for hundreds of games.

Hotline Miami (was 10 $ i got it)

The Elder Scrolls V: Skyrim and it's expansions and DLC. Definitely an award winning game like it deserves to be. I will say the voice acting is a bit repetitive, because most of the characters sound like they not only have the same voice actor, but also have the same voices, and if you travel around a lot you'll see this for sure in a lot of places. I will say though, the gameplay experience is well done, though sometimes glitches can get in the way if you're not careful. However, don't expect typical RPG gameplay, as the only actual RPG stats are Health, Magicka, and Stamina, and the rest of what you're capable of is determined by Skills and Perks gained through leveling up, each Skill also having their Leveling system. I will say one thing, the choice of races may or may not be varied. The best races are Orcs, Khaijit, Argonian, and Nord (The native race to Skyrim), but I think there's a bit too many Elf and human subspecies to the point it sometimes strikes me as bland choices in some areas.

Regardless of the complaints, Skyrim is an awesome game indeed, and do not let it's flaws deter you from playing it at all, for even with it's flaws, it's one of the best games of this generation.