One thing that annoyed me a bit.
Mels grew up at the same rate as Amy, then when it comes to after that she regenerates and becomes the River we all know, all is well and good. How come she stops ageing at this point? Seriously, while she could regenerate she aged and now she can't she doesn't? It makes no sense even in a fiction story.
As others have pointed out I felt sorry for Hitler at the end there, no one likes being stuck in a cupboard.
She also said:
I think I'll try to make myself appear a bit younger as time goes on, just to freak people out. I thought it was a bit of a poor "breaking the forth wall".