1st one ? Not much :D While I really tried to finish Witcher 1, it had so many glitches and gameplay issues I didn't like, I never managed to do it.
Witcher 2 is a whole different story though. Amazing graphics, both in cinematics and in game, a fun combat system that requires some skill (quite a lot actually, but you get to learn) to get it right, if you just mash the buttons you will die. It's constantly being patched and updated, there's a huge free patch coming in march that should deliver up to 4 additional hours of gameplay. It's not a dlc, everybody that owns the game will get it at no charge.
But, the most amazing thing about the game is how mature it is. With a few exceptions, the fantasy rpg genre consists mostly of very cliche and naive stories and characters, you go around in a shining armor, decapitate bad guys and rescue the princess. In Witcher 2 you get to make a lot of mature choices and they rarely are black and white, and most of the time there are no good guys, just the slightly less bad ones.
In the 1st village you reach, Flotsam, at some point you're faced with a choice of who to ally with - Iorweth, an ******* elf terrorist that slaughters people without hesitation while throwing around accusations of racism and Vernon Roche - an elf hunter of sorts, leader of the Redania secret police (you get to meet the guy in their dungeon while they're interrogating you). And depending on what you do, consequences can be brutal - on my 1st playthrough I sided with a different guy and completely missed this scene, but on the 2nd one, at one point I found myself in the middle of a pogrom, with elves and dwarfs being the targets.
The game is mature not because you get to see a tit or two (great sex scenes btw, a lot better than in Mass effect or witcher 1), not because of the rampant swearing (though I play in Polish so don't know what "western" censors did to the dialogs) but because of the plot and a "actions have consequences" approach. This is not a game where you seemingly have a ton of options only to find out they all lead to the same conclusion - here there are multiple endings and depending on the choices you make in the 1st chapter, you get to play the 2nd one in one of 2 places. To see them both and do all the quests you have to finish the game at least twice.
Then again I did read all the books 3 times (sucks for you if you're not speaking Polish) so I'm not sure I'm objective enough ;)
as an added bonus: the 1st in game sex scene ;)

The Witcher 2 SEX Scene Ultra Setting (Adult Contents & Nudity Warning*) - YouTube

Wow sounds good, I see its available on both PC and 360, not sure which is the best version but will put it at the top of my list anyway.

The main difference is the graphics - the xbox version, while by many called the "best looking xbox360 game"(which is yet to be determined really as the game is not out till march) looks like the pc version on low. If you have a powerful enough machine, I suggest you play on pc. Also if you have a monster machine, the kind regular mortals don't really need for anything, you can run the game with ubersampling - something my i7 and gtx580 can't handle well ;)
But on the highest possible graphics setting without the ubersampling, I had people that are completely ignorant of video games stop and stare. Hell, when i bought the game and brought it home I had a couple of friends over and "I'll only turn it on for a moment to see how it works" turned into "3 grown men and 2 grown women are hypnotized for 45 minutes by the sheer beauty of the game"
Apart from the graphics I don't think there are any differences.
Yac.

Tore pretty much hit the nail on the head!

I like the fact that Witcher 2 doesn't have a karma system. They explained it as "You're just a hero that's reacting to situations he's put in."

Also, the intro....

Now those are very impressive graphics.

At the moment I'm on a medieval/fantasy type fix and really digging Skyrim, and reading the Song of Ice and Fire novels, so this does interest me a lot.

Just finished playing Runespell Overture and Call Of Duty: Modern Warfare 3. Runespell Overture is a fun poker rpg style game, and will keep you entertained quite a bit. Call Of Duty: Modern Warfare 3 single player was good in my opinion. Other than being short, it had good action and an interesting story (it was written by Paul Haggis, a favorite director of mine).

Love the COD games but have heard this is a bit short, will be getting it soon. Also I'm going to pick up Gears of War 3 its going really cheap at the moment and loved the first two.

Gears of War 3 is easily the best in the series. Horde mode is tons better, The story is fantastic and it's the only Gears game that I actually enjoyed playing the Competitive Multiplayer.

While COD:MW3 was fun, it was short indeed. I played on Normal on my first play through and finished the game in 4.5 hours. It was a great 4.5 hours indeed though.