Enterprise general failure was because of the forced temporal cold war. They didn't have the guts to do a real prequel they needed a reset button there, so they have an excuse to whatever they did. Just look how awesome the characters have become during the shows 3rd and especially 4th season. In the right hands the shows 4th season showed how awesome could have been the series.
Enterprise's failure was due to lazy writing and the public's boredom with it. Throw in a difference of opinion on why the show was a prequel(studio wanted a show with no baggage that was accessible to all viewers and fanboys expected it to explain everything they saw in later shows) and you had a disaster waiting to happen.
The only thing the 4th season showed was that some fanwank could excite the few fanboys left watching the show.