I've finished season 3. It's great.
This is my most rewatched season and so some episodes were hard to get through, not because they are bad, but because I have seen them so many times and have them practically memorized. For example, episodes like Yesterday's Enterprise which are mostly about plot twists are not so much fun when you know everything that happens.
Some of the mediocre episodes have taken on a special significance on the umpteenth watch. Like Jonathan Frake's hammy performance in A Matter of Perspective. "You're a dead man, Apgar!". One of the best unintentionally funny moments in the series.