I have occasionally liked individual episodes of TV shows. I can't think of a series where I liked every episode.
There were, for example, several episodes of Star Trek Next Gen that I could enjoy. Picard gets a "virtual reality" wife and children on a doomed alien planet, that was pretty good. Picard insists "There are... FOUR lights!" that was also a pretty good episode. There was an episode where four junior officers were chumming around, even having their own junior officers poker game. That was notable for the lesson Whorf taught one of them. In the same series there were also quite a few that were just drab. I mean, Barclay gets a flu shot, and Data's pet cat Spot turns into an iguana. Give me a break. And oh look, another holo-suite episode.
DS9 occasionally brought us an interesting episode. They did a riff on "The Man in the Glass Booth" that worked pretty well. And Whorf marrying Dax was interesting. And when Sisko kicked butt, that butt was officially kicked. But a lot of the episodes were fairly forgettable. Hey it's another wormhole-living-entities episode. Yawn.
Dr. Who used to produce a fun episode once in a while. They've choked that off pretty carefully now.