Except this is how 11 has been for pretty much his whole run, manic, overwhelming joy and wonder that covers up a darkness, an abiding anger and a willingness to kill. Look at how he was in Victory of the Daleks (though the Daleks always bring out the worst in all the new-Doctors), Day of the Moon (he essentially hypnotized the entire Human race to commit genocide against a race they don't even know exists), How he acts towards Uncle in the Doctor's Wife, Good Man Goes to War is an obvious one, the list goes on. Yes, he's being a bit more 'hands on', but I think that comes in part with how he's realizing that he has *always* killed people, always been responsible for others deaths, and now, rather than letting other people kill them or letting them kill themselves, he is taking it into his own hands to an extent.
Don't be tricked by his exterior, 11 is by far the darkest Doctor of the New run, and is pretty far up there even with respect to the old run. He pretends to be a big child, because he knows how old he is and is trying to fight the effect his age has on him. And as the last few series have shown, it's a fight he may very well be losing. (Valeyard anyone???)
I agree with this completely. You said it better than I could.