In terms of external threats, it would have been fine if Voyager remained episodic. After all, given their single-minded course, it makes sense that they would enter alien territory at the beginning of an episode and then leave it by the end. Internally, though, there's no reason the show didn't become more serialized. The vessel had a smaller crew than any previous Trek series, and yet we rarely got to know any of the characters outside of those in the main credits. (And even a few of them remained, or eventually became, ciphers.)
The Maquis/Starfleet tension quickly evaporated (as did later, Equinox/Voyager tension). This was replaced with a vague sense of the ship's crew becoming a "family," but this concept wasn't really developed, either, and given how little we knew the characters onboard the ship, often seemed false. It's hard to believe how unexplored the psychological consequences of being cut off from home (and cut off from much relaxation) were on the series. (Then again, despite some weak gestures about holodeck rations, the fact that the crew was small and getting smaller didn't seem to have an effect on the proceedings).
Most of the time, it was TNG with the names changed. This was fine, I suppose, but a waste of the initial premise.