The premise of Voyager is great - a single Federation ship in the Delta quadrant with a mission to get back home should have been a perfect playground to test the Federation’s principles. But the problem is that Voyager’s scripts didn’t really do anything with it.
Interesting moral questions come up and are immediately abandoned. Do you trade technology for safe passage? Bend your ideals to survive? They can't decide - they give replicators to the Kazon and then fight them in the same episode. They ally with the Borg, to drop it half an hour later. They fight Species 8472 and then team up with them. Nothing sticks.
The Maquis are another wasted idea. A mixed crew should have been a constant source of tension, but apart from Seska (and Chakotay’s embarrassing plotlines), it’s ignored almost entirely.
Most of the characters are weak or static. Torres is always angry, Chakotay is neutralized and neutered, Kim never advances, Paris constantly resets, and Neelix kills the tone. Only characters with real growth are Doctor and Seven. And Janeway is whatever the plot needs her to be - a scientist, a moral absolutist, a pragmatist with no consistency - sometimes in the same episode. Even Picard, constrained by Voyager's scripts couldn’t have saved this.
Voyager failed because it didn't commit to it's own premise.