Hmmm. That was a mixed bag. On the whole, I'd say it was a better than average conclusion for a New Who two parter, but it was a shame about the dodgy CGI monster. Matt Smith did an excellent job of playing the Doctor and the Ganger/Doctor, and I loved the jelly babies moment.
The twist ending throws up lots of questions. Just how long has Amy been a Ganger, and who made the switch? And why? Also, how can the Doctor spend most of the two episodes arguing that the Gangers are living beings and have rights, then kill one of them in cold blood? I get that he'd be angry about the deception, but I'd have been much happier if he'd simply locked her up until he could work out what to do with her. I suspect this was just lazy writing - it would be too messy to have two Amys running around, so the Ganger had to go. Still, it does seem very out of character for the Doctor to simply kill her.
Still, this reminds me of the Doctor's rather heavy-handed solution to the Silents problem, and I'm wondering if this might be a theme that will play out later on. On the surface, the 11th Doctor seems to be a more jovial chap than the 10th, but he does seem to have a very dark side to him. I think he needs to be taught a lesson, and I hope he will be.