One word: Mount & Blade: Warband

thats 3.5 words lol, mount & blade was a very good game I hear warband is mostly better and has multiplayer that is fun so good recommendation. 

So far, I already bought me Machinarium and I´m definetely interested in The Witcher, KOTOR (I already had this one on my mind) and Freedom Force.

Among all the others, I need to inform me deeeper on those games mechanics, strong points and weaknesses. Specially when there's little time to play and you want to have the best experience possible in it.

Thanks to all of you guys! You are helping me big time.

2 things that I'm surprised no ones mentioned, lol.

Since graphics aren't an issues with you get Deus Ex: GOTY edition. See what the hype is about for his Epic Mickey title.

Second I'm not sure how you feel about Steam, when I got a good PC to go with my Wii, I signed up for Steam and TO ME it was a good choice. The game deals, Steam Cloud, etc.

Are you trying to get a job?  Why are you getting random people to recommend you?

I second this. Steam is very good and is worth taking a look if you haven't got an account. You can find some brilliant indie titles on there too.

For what you say, I am under the impression that in english you use "recommend" only work related. I'll look it up. In spanish it just means you are asking for advice, for a word of wisdom.
Fortunately, people got it right.

Not released yet:

• Civilization V - It's a turn-based strategy but you'll definitely want to try it out. The series is so addictive and good. Coming out next month with a demo before the full version. You can also try Civ IV if you want something now.
• Shogun 2: Total War - A mix of real-time and turn-based strategy, the campaign will be turn-based while battles will be real-time. You can probably skip battles altogether, let the AI handle them for you. Coming out next year.
• Crysis 2 - The next graphics king. 'Nuff said. Also, the first one played out pretty well so this one should too.

Already released modern games:

• Total War series - Read my description for Shogun 2 above and if you got interested, you can try these. Rome is the favorite of many.
• Crysis - Not a jewel but something you WILL want to marvel at with your shiny new graphics card. And I think gameplay's fine too. There's a demo available if all you want is try out the graphics.
• Dragon Age: Origins - I suppose you know this one already. Anyway, the PC version is superior thanks to an addition camera angle (which is great) and mods.
• The Elder Scrolls IV: Oblivion - You've played this on consoles, now try it with mods on the PC. You won't be disappointed. I personally recommend Oscuro's Oblivion Overhaul if you want to see a huge difference once you've played a short while (it's not a visual difference so you won't actually see it, you'll have to experience it).
• Titan Quest ( Immortal Throne expansion) - An excellent Diablo clone. An action RPG in case you were wondering.
• The Witcher - I haven't had the time (or the will) to try it myself but it is pretty much considered the best RPG in a while.

And older games:

• Baldur's Gate series - Both are worth experiencing, and especially the second one is considered a classic. You'll love it.
• Deus Ex - A combination of a first-person shooter and an RPG. You don't want to miss this one.
• Operation Flashpoint - Feel the war.
• Wolfenstein: Enemy Territory - A free multiplayer. Its predecessor, Return to Castle Wolfenstein, either invented or popularized the class-based, objective-based multiplayer gameplay you surely know even today. Tons of custom maps (and small mods that tweak gameplay) available and actively in use (which also means you'll have quite a bit to download when you join a server, though it should be a couple of minutes only to get into action).
• The Elder Scrolls III: Morrowind - I haven't had the time to try this one either but many seem to think Oblivion lost much of what made Morrowind so great.
• Neverwinter Nights - Another great RPG I haven't been able to test myself.
• Planescape Torment - ...And yet another one.

If you don't mind going old school, get Planescape: Torment, Ultima VII, and the Fallout games (even though 3 isn't so much old school ).

a game called "And Then There Were None" .