I played it last night for a bit. It was fun. I wouldn't call it amazing, but I enjoyed the demo enough to want to go back in and play it some more. I enjoyed hitting timestop and running up to guys and shotgunning them in the face, then starting time back up and watching them fall.
I wish there were options for taking people's weapons (like in the video they showed) and more options for melee instead of a weak-looking weapon swing, but overall I think the demo is definitely worth the download.