So does what happened mean that Matt Smith will be the last actor to play Doctor Who?
Not a chance. They'll retcon it if it ever becomes a problem, which it won't as they'll never reference it beyond this two parter, or this season at most.
I'm not keen on Amy Pond's character, and the Doctor is a bit on the manic side.
The aliens were good though - I like the idea of people not being able to remember them, that's clever.