The binding of isaac is an awesome game. If you don't already have it, I recommend checking it out.

Bastion, Batman games, Deus Ex, Xcom, or the first Bioshock. All of these games except for Deus Ex have a demo.

red orchastra 2 is a good FPS

I second Xcom. Also Mount and Blade: Warband if you like medieval style hack 'n' slash stuff.

Thanks guys! I'm definitely gonna check out the games with demos. They all sound/look great so far! Keep em comin'! :)

Try Endless Space if you're into strategy, it's even conveniently free for the weekend. I also second Bastion.

Oh bejeesus. There's a ton of games out there. For FPS, there's the S.T.A.L.K.E.R games, Team Fortress 2, Red Faction, Half Life, Borderlands. For RTS, there's the Total War games, Warhammer 40K, Flotilla, Sins of a Solar Empire. For RPG, go with Skyrim, Mount & Blade Warband. For horror, go with Penumbra, Amnesia, Slender, SCP Containment Breach.

Check out GOG.com for a lot of older games, too. They also put out newer indie titles for great prices and no DRM.

Recettear: An Item Shop's Tale is pretty good from what I've seen so far in the demo :) I also second the recomendation for Mount & Blade Warband and The Binding of Isaac. Vampire the Masquerade Bloodlines is good aswell with the unoficial patch but no demo for that one.

I second Vampire the Masquerade Bloodlines and Skyrim, if you're at all interested in MMOs I find Dungeons and Dragons online and Continent of the Ninth Seal are fantastic, both are available in the Free to Play section of the steam shop. Have fun!

If you like platforming, I'd say Psychonauts for 3D or Rayman: Origins for 2D. Both were great games!
For your FPS needs, I second Borderlands. I also love The Ship! It's definitely not everyone's cup of tea, and at this point it's basically been replaced by Bloody Good Time, but it might be worth checking out? Maybe?
Otherwise...Secret of the Magic Crystal? LOL!

Honestly, fuck Skyrim. It's an entry-level rpg loved by people who don't know much about crpgs, but it honestly doesn't hold up. Fallout New Vegas is where it's at. It's a pretty decent game even without mods, but the expansion packs are amazing. Other than that, there's not much entry level crpgs that I can recommend for the pc.
If there's anything that you absolutely must play, it's Saint's Row 2. Imagine how batshit crazy the GTA games are, then multiply it by a hundred. Think running and gunning people is pretty insane? Well try running into traffic and spraying entire neighbourhoods with feces for insurance fraud.

Yeah you should definitely play The Binding of Isaac. Pretty good game.

Natural 2 is a good game. It's a fps/rts hybrid game.

If you have the time and are interested, Still Life is a pretty great adventure game with a good story.