IIRC the show runner changed at the same time that Matt Smith became the new doctor. The tone change is pretty noticeable pretty much right at the start of Seas

IIRC the show runner changed at the same time that Matt Smith became the new doctor. The tone change is pretty noticeable pretty much right at the start of Season 5 in my opinion, even as someone who enjoyed pretty much all of it before and after (although I haven't kept up with it the past few years mostly due to my TV watching habits having changed due to different life circumstances).