ENT made a handful of changes to established continuity in TOS and TNG, but for the most part the only continuity it messed with was "fanon/licensed continuity". An example would be the Klingon ridges. An unofficial explanation was provided in a book somewhere, and at that point people just accepted it because it was never really established in the official continuity. Suddenly it is established officially though, and people might get a little annoyed about ENT messing with 'established' continuity. Not saying there aren't changes in ENT, but I don't think there are drastically more than, say, any other ST series.
There were other things in "Enterprise" that messed with continuity, though. I could deal with the different Klingon look; but, for example, the show took place about 150 years before TOS, yet, they had "phase pistols" and "phase cannons".
However, in "The Cage" which takes place just a few years before Kirk's 5-year mission, they had lasers.
The writers changed the term between times, because the term "laser" had become common knowledge by 1966.
Also, in the "Enterprise" era, Earth would just have been coming out of the last of the Romulan Wars. Yet, they encountered a Romulan vessel and didn't recognize the ship. I can't remember if they met the Romulans face-to-face, but if they did, this, too, was a continuity error. In the first-season TOS episode, "Balance of Terror", it was established that, despite the brutal war they fought, neither race had ever seen the other until then. There were other errors, too, and it just bugged me. You don't screw with the details, y'know?