Many of the comments here are too enthusiastic, and some are far too critical. But a small group hit the nail on the head: this a very good film that is definitely worth watching. The highlight of the movie is the beginning, there is no doubt about that, but the rest is still good. While the relationships between the characters may seem "awkward" to some, they come off as very human, and not contrived. Human beings are awkward. The ending on the other hand, is a little contrived, and goes a little far in terms of just how much the viewer will believe. But it's not a bad ending and as another comment said, it is very exciting.
Very good script and very good acting. Funny, clever, exciting. I gave Quick Change an 8 out of 10, and I was even tempted to boost it to a 9.