Yeah, it ran great on my system as well. I think it actually ran better than Left 4 Dead 2. The graphics aren't amazing, but they look a lot better than the old Portal, and the significant increase in animation all over really makes a difference.
I've just now beaten the game, after some serious marathon gaming sessions. I died a few times, but it all felt like my own fault, which is good. A few of the later puzzles really were hard for me, usually because I'd overlook some simple piece to the puzzle). Some of them just have so many steps to reach the solution that you can get lost in the details. I don't consider this a bad thing, it's nice to be challenged.
As for the ending, it was hilarious, somewhat surprising, but also left me feeling a little empty. I wanted a bit more. Also, for those hoping for some Half-Life 2 tie in, you can stop. Black Mesa is mentioned occasionally both by the characters and by things on the walls, but absolutely nothing to really tie in with the current story going on in HL2.
I think I wrote this post with no real spoilers, but if anyone thinks they're getting spoiled, I'll edit.