isn't that bad, it's just not all that good.
It was TV. Not a medium known for its depth at the time, or now for that matter.
What it is, is Star Trek
did (and does) good and bad episodes, and they're all Star Trek
. Even the movies do the exact same thing as all the series have done. Good episodes, and not so good ones. They're all Star Trek
, so they're all good.