Don't put all the blame on RTD, blame the script editors that didn't smack him upside the head.
I enjoyed the episode, myself. The Doctor being reduced to a baby-like creature could simply be explained with the fact that he's an alien. Time Lords only stop aging when they turn into little Gollum-like things.
Although I was hoping for a better explanation of Utopia than what we got. A trap to turn everybody into Pseudodaleks? I was hoping for the next season to talk about that, and show the creaton of the next universe. But nope, just everybody getting turned into faux-daleks in spheres.
Still, I'm giving this a 8/10.