Well, when I first saw footage of this game around E3 I was really interested but not really looking forward to it as I assumed my system couldn't handle it. Well, now that I've played through the demo (several times) this game has shot to the top of my list of most-wanted PC games.
The game uses the Source engine which is really easy on older systems (Half Life 2 looks great on my computer) so the game manages to look really great despite my Nvidia 5200 FX card. I was not able to get Elder Scrolls IV: Oblivion due to that game's requirements but this game promises a similar, though more straight-forward, experience. I have played Oblivion, however, so I can definitely say this game does some things better then Oblivion ever did.
The combat is far superior. More attack animations, greater variety of weapons (or so it seems, theres about half a dozen very different weapons in the demo and I'm sure theres more to be found in the rest of the game) and smarter enemies. Also, the game uses physics extremely well. You can pick up a crate (and your hands actually grab the crate, unlike Half Life 2) and hurl it at an orc sending him off a huge cliff. Very satisfying. Or you can kick the support beams of a balcony and have the whole thing crash down onto a group of enemies. The whole thing was just really impressive and I can't wait for it to come out.
One minor complaint about the demo was none of the cinematics worked (no Ubisoft logo, no intro, nothing). I assume this is because it uses Bink video ( I seem to recall having problems with that before) or its a glitch of some kind. Either way, great demo and definitely worth the download.