Enterprise failed to captivate the fans like TNG, DS9 and even VOY managed to do. And it's all because of the quality of the writing.
You must not have watched TNG, DS9, or VOY when they were first run. TNG honestly (and rightfully) got blasted for it's TERRIBLE first two seasons; and actually didn't start receiving some positive mentions until "Yesterday's Enterprise" in Season 3.
Similarly, I suppose you forgot the "DS9 is too bland/dark/npt GR's 'vision'..." cries from Star Trek fans during its first two seasons too.
the simple fact is - there isn't a post TOS/TAS Star trek series that didn't have god-awful writing during its first two Seasons, and actually, at least ENT has a couple really decent episodes from its first coupl,e of seasons ("Silent Enemy"; "The Andorian Incident" "Fallen Hero"; "Dear Doctor" to name a few from S1 and "Minefield"; "The Catwalk"; "Cease Fire"; "Future Tense"; "First Flight"; and "The Expanse" from S2).
Season 3 of ENT overall was on par bwith the best of TNG S3 and (IMO) S4 was some of the best Star Trek stories done since TOS S1.
Now, I'm not disagree that ENT failed to capture/maintain enough of an audience, but honestly, and overall, it wasn't the writing or the production values -- it was most likely due to the fact that in 2001 - there had been (counting TAS) - 25 full TV seasons of Star Trek material produced to date; and 9 full length feature films feature Star Trek characters; an while I know this will come as a big surprise to hard core Star Trek fans; but after a while the general TV viewing audience says "enough" to a given set up. That's pretty much what happened by the time ENT hit the air waves; and I think it would have happened to whatever version of Star Trek (in the then 35 year old Star Trek 'Main' Universe) Paramount tried to put on TV.
Overall, I say, episode for episode, the writing on ENT was above what we got from TNG and about on par with what DS9 was doing for it's first 4 seasons.