Please find enclosed, Charlie Brooker's point about David Tennant's Doctor that I agree with entirely.
Ecclestone was dark, angry and cynical and when something broke through his shell, like in the WWII episode, he had a childlike wonder that he clearly felt he'd lost.
Smith's Doctor was so ridiculously youthful looking that he often SEEMED immature, not in an irritating fashion (although I did sometimes find him irritating in general) and I felt like he was always learning about things, constantly discovering new aspects to the universe.
Tennant, though, was just... 'oh it's one of these, they still work by pressing this button? *beep*'