I enjoyed the singing – I thought it gave the episode a bit of (more) emotional impact.
I think the different leaf was probably a continuity thing, it looked big and plastic in this episode, and a bit naff, I thought.
Did anyone else think the Doctor’s reaction at the very end was telling? He says something like “you did it all yourself”, whilst looking deeply concerned. I think it was more than just amazement that Clara did the leaf thing. I think he can see that she’s more than just a normal human, and is worried about exactly what. I don’t think he believes that it was the ‘infinite possibilities’ of the leaf that is what got the job done in the end, but I think it connected to his very strange reaction last episode to the leaf.
I also think that the ‘things look different’ line was more significant than just expanded horizons, but I’ll wait and see what exactly it is!