It's just silly mad fun. The demo is long enough to really get a taste for the game. It seems from the reviews I've read that it's a love it or hate it kind of thing. There are enough things going on in the environment, the "matrix-like" bullet dodging standoff, and the "close up shot" thingy to keep things interesting. Pretty much everything in the game that isn't a building or something else very rigid is destructible which is great fun.
For grins, try the demo a couple of times and try shooting people with the aimed shot in the knee, groin, eye, hand, foot, etc. All sorts of different animations.
Great fun indeed but YMMV.