i have it at the moment (borrowed it off a mate for a few days, he completed it in an evening, saying that though, apparrently there's a lot more to it, it's just he completed the first game, there's a directors cut and more!).
so far i've really enjoyed it, it's very tongue-in-cheek, lots of gratuitous swearing and violence, but it's done in a funny way, not trying to be 'cool' by doing it).
if you use it, don't use the wii zapper, i'd HIGHLY recommend buying the 'hand cannon' gun accessory (it's the official accessory for the game). it makes it a LOT more fun! x