I could play it just fine on medium-high options on a laptop and on high on a dual-core PC with a 8800 GT at the time. I had to put up with ~30fps, but I guess it was acceptable.
I actually thought the single-player was very good to amazing (especially the alien/snow levels), but the multiplayer just wasn't any fun, so it's because of that that it never picked up in my opinion, not that people couldn't run it necessarily. If it were really fun, people would play it on low if they had to...
Kind of sad, but the game had the exact same fate as Far Cry. The Crytek people just don't seem to be able to deliver a compelling multiplayer experience.