For me personally it is less a question of what I consider fun. I don’t use that phrase. It is just an observation of mine that in about 90% of the cases when I read this phrase written by others it is about a score that I consider rather bland, uninteresting and sensationalistic.
In best case, yes, this can be kind of a guilty pleasure.
That does not mean that fun isn’t a feeling that I connect with film scores. But even when I have fun while listening to a particular score, I would never use that phrase “This is a fun score.” because this is usually used to say that people have very low expectations to this music.
Other people might have other experiences. That is why I asked the question.