I was very, very happy with "The Eleventh Hour". It became apparent early in previews that Matt Smith was going to be excitedly eccentric and I was worried it'd be in the same vein as Ten's earlier seasons. Luckily, Smith dialed the quirkines way up, to the point where it actually differentiated him from Tennant in and of itself. I was very impressed with his performance and this episode alone eroded any doubts and/or cynicism I held about Matt Smith.
The episode, as a whole, was very good. Moffat always delivers, though, so that wasn't much of a surprise. I'm not sure how I feel about Karen Gillan as Amy Pond yet, because her relatively strong performance is being overshadowed (for me, at least) by the fact that she is very, very, very pretty. That was my impression of Martha at first too, though, and I grew to despise her before long. Hopefully Amy's character will come into her own throughout the season...I'm sort of annoyed that she has her own Mickey (who's equally annoying), however.