You know, I tend to sort episodes of TV shows into three different categories.
1. Good and worth rewatching.
2. Good, but not worth rewatching.
3. Bad, and not worth rewatching.
I suppose there could be a bad episode which is worth rewatching, but I'm not sure what it'd look like. Maybe an episode which I personally disliked, but one which was crucial to the show's overall storyline.
There probably should be a middle category of "ambivalent quality; not noticeably good or bad", but that generally leads to "not worth rewatching".