There are objective measures that can be looked at beyond one's subjective enjoyment to make an evaluation. For example, I like the movie Ultraviolet. But it's story incoherent, the CGI is horrible even for 2006, the acting is wooden, and by any standard of filmmaking it is a bad movie. Those aren't arbitrary measures. But for some reason I enjoy it as stupid mindless fun.

I don't need to justify my enjoyment of that movie by claiming it is "good" because it isn't. It is very possibe to distinguish between the overall merit of a game, movie, show, etc. and one's own subjective enjoyment of it.