Short story, I have a new PC coming and I want to get back to PC exclusives that I missed before because my old PC couldn't run them very well.
 
Games I've already played or already have include: Starcraft 2, Civ V, STALKER Call of Pripyat, and Majesty 2.
 
Are there any sleeper hits from 2009 or 2010 I've missed?  I'm interested in any genre besides MMO.

The Witcher, originally from 2007, I believe..  but if you haven't played it yet, you definitely should, especially with the sequel coming next year.

Sleeper hit? Amnesia: The Dark Descent

If you like strategy/RTS, Starcraft and Company of Heroes are both winners. 

" Sleeper hit? Amnesia: The Dark Descent "

" The Witcher, originally from 2007, I believe..  but if you haven't played it yet, you definitely should, especially with the sequel coming next year. "

" If you like strategy/RTS, Starcraft and Company of Heroes are both winners.  "

Not sure if it will be your thing, but the best games I've bought this year were Minecraft and The Polynomial.

I made a list of all the "best" PC games over here in this thread. Been trying to get it stickied so people can use that instead of having the forums getting threads like this all the time, but it just keeps getting pushed down the list. Check it out anyway. It doesn't go into old old games, but it covers pretty much all the big ones in the past 10 or so years that can still be easily found online.

-metro 2033 
-Supreme commander 2
-ehh...starcraft 2 is all you need really. Everything else is icing on the cake. (I've been playing that game since launch 5 months ago on a daily basis)

" VVVVVV is what Super Meat Boy has been compared to on the PC a lot. It's an excellent platformer with excellent music and all the sadism / masochism the genre can provide. "

" Not sure if it will be your thing, but the best games I've bought this year were Minecraft and The Polynomial. "

- Crysis 
- Crysis: Warhead 
- Minecraft 
If you haven't played Oblivion or Fallout 3 on PC, they're a must, even though they aren't PC exclusive.

You should eventually play Civ 5. But to avoid the headache it continues to give me, I'd consider waiting until the next patch.

Mafia II 
Need for Speed: Hot Pursuit (Not an exclusive, but it is really pretty on the PC) 

Recettear 
Killing Floor 
Machinarium 
 
They aren't very demanding games, but they are fun.

• The Witcher
• Men of War
• Anno 1404 / Dawn of Discovery
• Dragon Knight Saga
• Dragon Age & Awakening (if you haven't already)
• Dawn of War 2 & Chaos Rising
• Empire TW and/or Napoleon
• Lionheart: King's Crusade

" Recettear Killing Floor Machinarium  They aren't very demanding games, but they are fun. "

Dragon Age Origins, I know I must be the billionth person who said this but the PC version is vastly superior to the console version.

Download Alien Swarm.  It's free.
 
Dawn of War II is pretty cool.
 
Plants vs Zombies is a lot of fun, but you could probably have played that on your old PC.
 
Metro 2033 is a pretty cool game if you can run it.

I'd suggest Team Fortress 2. It's an extremely solid entry on Steam, and it usually goes on sale once every 6 weeks or so. Also, as stated earlier, Minecraft; It'll run on most computers, but you should get it while it's cheap, since all the updates/upgrades will be free, but it gets more expensive with each iteration.
 
As for other games, I usually just keep an eye on Steam, and demo anything that goes on sale.

" -metro 2033  -Supreme commander 2 -ehh...starcraft 2 is all you need really. Everything else is icing on the cake. (I've been playing that game since launch 5 months ago on a daily basis) "

" - Crysis - Crysis: Warhead - Minecraft If you haven't played Oblivion or Fallout 3 on PC, they're a must, even though they aren't PC exclusive. "

" You should eventually play Civ 5. But to avoid the headache it continues to give me, I'd consider waiting until the next patch. "

" Mafia II Need for Speed: Hot Pursuit (Not an exclusive, but it is really pretty on the PC)  "

" Dragon Age Origins, I know I must be the billionth person who said this but the PC version is vastly superior to the console version. "

" Download Alien Swarm.  It's free.  Dawn of War II is pretty cool.  Plants vs Zombies is a lot of fun, but you could probably have played that on your old PC.  Metro 2033 is a pretty cool game if you can run it. "

" I'd suggest Team Fortress 2. It's an extremely solid entry on Steam, and it usually goes on sale once every 6 weeks or so. Also, as stated earlier, Minecraft; It'll run on most computers, but you should get it while it's cheap, since all the updates/upgrades will be free, but it gets more expensive with each iteration. As for other games, I usually just keep an eye on Steam, and demo anything that goes on sale. "

Mount and Blade: Warband is fun even in Singleplayer.

" I made a list of all the "best" PC games over here in this thread. Been trying to get it stickied so people can use that instead of having the forums getting threads like this all the time, but it just keeps getting pushed down the list. Check it out anyway. It doesn't go into old old games, but it covers pretty much all the big ones in the past 10 or so years that can still be easily found online. "

" @sins_of_mosin:  maybe it would be a good idea if you actually listed out what games you've already played....? "

" @sins_of_mosin: Alright, so as a rule, you're looking for some decent single-player games that are PC exclusives(I'm using the title of the thread as a point of reference). You're not too big on horror, but you definitely seem alright with Strategy and Shooter genres. Hmm...  
 
If you're alright with dungeon crawlers, and you haven't gotten completely sick of Diablo, I'd say to give Torchlight a try (alternatively, you can just wait for Torchlight II to come out.) 
If you haven't already picked it up on XBLA (non-exclusive, I know) I'd check out some of the Telltale adventure games.  Any other preferences? It can be kind of hard to find "groundbreaking" PC exclusives these days. I'm kinda getting back into PC gaming myself  (The GF commandeers the 360 for Netflix a lot) so please pardon any non-exclusives I've thrown out.  "

 anything with the word tycoon at the end and that's about it

If you liked Majesty 2, you may enjoy Settlers VII if you can get past the you-must-always-be-online bullshit. There's a quicklook on it if you wanted to check it out.

" The Witcher, originally from 2007, I believe..  but if you haven't played it yet, you definitely should, especially with the sequel coming next year. "

" @WinterSnowblind said:

" The Witcher, originally from 2007, I believe..  but if you haven't played it yet, you definitely should, especially with the sequel coming next year. "

I played this game for like 15 hours straight the day I got it, but I can't get myself to play it again some reason. "