The series finalé tainted the series as a whole. Starting with the last episode of season 2, Enterprise really found its footing and became an excellent Star Trek series. Seasons 3 and 4 were nearly as good as TOS and TNG in their primes. While I greatly prefer stand-alone episodes for Trek, Enterprise did the serial format very well. They had set up the story arch to prepare for the Romulan war, which could have been very exciting and could have really fleshed out that part of the Star Trek universe. I think it would have been great. Shran was also supposed to become a regular in season 5, which also could have been quite interesting. But all of this was tainted by the finalé, which felt like a mediocre TNG episode. "The Pegasus" was an OK episode, but it felt shoehorned into Enterprise. It felt like the were trying to say that Enterprise wasn't good enough by itself to have a final episode that would be good. It felt like they needed a TNG episode to bail them out. I understand that the ratings had dropped because of the mediocre first two seasons, but they could have at least allowed it the dignity to have a series finalé that was an Enterprise episode rather than a TNG episode. Voyager's ratings dropped towards the end, but they allowed it to have a dignified ending. TATV was a stain on an otherwise great season.
Yep, this is all pretty much common knowledge for the last 20+ years.