Briefly skipped over to the bottom 5 thread for inspiration. I actually like those:
A Matter Of Time
I'll agree that it is in fact a pretty mediocre, convoluted episode that leaves lots of questions (I've asked some of those myself on the forum in the past), but I liked this one the first time I saw it as a teenager ('cool! Time travel and an even more advanced future!') and somehow that like has persisted, even though I have no good rational reason for it anymore.
Force of nature
I suppose this one is disliked mainly because it's such a blatant, heavyhanded analogy to our contemporary environment issues. I dislike it for that myself, too. But if I forget about that for a moment and only look at the episode for its own merits, there's actually not much I can find wrong with it - except perhaps with that handtying solution of warp 5 max, that of course was very quickly handwaved after that by just ignoring it or postulating that a new, less damaging version of warp drive was developed almost instantaneously.