Ya, Enterprise really dropped the ball with the whole Romulan thing. They really and quite definitively stepped on fans toes there.
However, Manny Cotto did try and save the show, but to be honest, unless it was a show filled with rap stars, it was doomed to fail on UPN. And note, UPN went the way of the Arseno Hall Show. When you cater solely to one class of people, you alienate all others. Enterprise was simply to intelligent for the viewing population of UPN and thus its ratings tanked and the show died. This, more so than the writing, killed the show.
Stepping on the toes of fans by destroying accepted historical cannon was simply to insulting for most fans to allow to slip by without a hissy fit. Brandon Braga and Rick really enticed a huge fur-ball when they pissed on the fans and TOS.