Siannah: Mount & Blade. Hard to describe just why....
Think of a Sid Meier's Pirates in the darkest times of the middle age, with an open world like Oblivion. You're free to go and do as you wish. And the combat is fresh, rewarding and challenging.
Yes, the game is a bit... let's call it unpolished. Still, I keep getting back to it and every time I do, the time flies by.
It can get a bit frustrating before you found out about the "dos" and "don'ts". I'm still just a newb even after my third attempt and reaching lvl 16, still standing away from forming an army or getting involved in the actually ongoing wars. Just running around with 8 other NPC, beating up street robbers and the likes, selling them to ransom collectors or even slave dealers - as soon as the enemies show some kind of military training, I'm getting my ass handled to myself. :)
And for Steam-haters: if you buy it over steam, you'll get an activation code with it. With this code you can actually activate the demo into the full game, so you don't have to use steam again.
Download the demo, try it out and see if you're getting into it. I'm simply hooked.
I bought Mount & Blade back when it was pre-Beta... It's a great game with a huge and active community for modding. Should try the Demo definitely and then buy it!