Let's be honest, Doctor Who has always had a, let's say "mixed" quality to its episodes. Even the best serials from the Classic Era has lots of wtf writing moments to it. The problem is that New Who seems to have a lot less "good" episodes as its progressed. The fact that people are actually nostalgic for Russel T Davis is astounding to me, since nearly every Who fan I knew hated him by the end of his run. Hell, I remember people being excited for Moffett when his run started, and now is seems most fans hate him. The new guy will probably be loved for his first two or three episodes, until the shit one gets aired.
On a related note, the best way they could handle the regeneration would be having the first thing Thirteen do is mention some random feature that got altered like Ten's "New teeth, that's weird." line then going straight into whatever Twelve was talking about before regenerating.