The Final Verdict
Even if you didn't like the silliness, the episode did have some interesting moments that questioned the Doctor's role as a hero. Clara clearly thinks he is one, same as any storybook hero -- like Robin Hood -- that she's read about. Robin's fine being remembered as a legend rather than history, saying "History is a burden; stories can make us fly."
But is the Doctor okay with being a legend? When Robin suggests that the Doctor is Clara's hero, he only responds "I am not a hero" -- which definitely seems to be the theme of the season. While the Doctor isn't sure, he has managed to save the day in every episode so far this season, even if he's had a lot of help to do so.
The fact that he's had so much help is kind of a problem, though: while the supporting cast has been great, we aren't seeing very much of this new Doctor in action. Even in this episode, where we've seen him more active than in previous ones, he only has equal time with Clara and Robin -- which isn't bad now and then, but it's odd to have several episodes in a row that way, especially just after a regeneration.
On the up side, however, this episode Peter Capaldi did a great job of channeling 7th Doctor Sylvester McCoy, who could similarly be both very dark and very silly. It was a combination that suited McCoy's run in the 80s... but does it still work today? This episode was almost too silly, but we're not ready to write off Capaldi just yet.