[ndsipa_pomu]

I agree about the difference between "great episodes with gimmicks" and "episodes with great gimmicks" and I'd put the SNW musical episode into the latter - it was them having fun with the whole premise and probably shouldn't be considered canon.

Personally, I enjoy it when writers/producers try out an experiment and have particular episodes that don't really fit in with the themes and expectations of the series as a whole, but they do tend to polarise people.

The classic example that I think of with regards to musical episodes is the Buffy The Vampire Slayer epsiode "Once More, With Feeling". Joss Whedon had been experimenting with different concepts, such as "Hush" (the opposite of a musical episode) and "The Body" (stunning piece of television in my view), so throwing in a musical episode wasn't completely unexpected, but that particular episode pushed forwards and resolving some major plot points with characters revealing deep secrets.

(It's interesting that the three Buffy episodes I mentioned are considered the best episodes despite them having dramatically different styles).