Since its inception, Enterprise had faced criticism from many angles. For one thing, it seemed to be capitalizing on the prequel trend that had been popularized by traditional franchise rival, Star Wars. For another thing, it seemed to take what most believed to be established canon and completely stood it on end. Add to that the fact that there "wasn't supposed to be" any other ships named "Enterprise" and most Trekkies built up a pretty solid defense against watching it. But forcing myself to go through this series was a surprising and educational experience.
Season one was what should have been the real smash-hit season of the series. If anyone was going to give Enterprise a chance, it was going to be here. Unfortunately, they made several mistakes that had no chance at overcoming people's doubts. The first redshirt should have died in episode 4, but our new captain fought for the episode to be rewrote so that he lived. Ferengi randomly showed up and our intrepid explorers and ambassadors of earth didn't even think to ask their names. Granted, they introduced the awesome idea of a Temporal Cold War, but we never knew any more about what happened with that than a dog knows what that waggling creature at the end of his butt is. There were several good bits; most of the characters I would grow to love, but overall I think it missed the point of what it was supposed to be.
Season two, after we got to know the characters a bit better, is exactly what a new Star Trek series probably should have been if it wasn't a prequel. There were some good exploratory bits, some new life and new civilizations, but they were still going where we had already been before. They were not taking advantage of the "back story" or the "lore" element of the prequel idea. Most of the stories were the kind I might expect to see the crew of the Enterprise-D or Voyager take on, so, while it wasn't yet what it should be, it was imitating a Star Trek series pretty well.
And then there was season three. Ah, season three, bless you for trying. It wasn't so bad overall, but instead of adding to the Temporal Cold War arc, it completely overshadowed it with what should have been just a footnote in the war at large. The Delphic Expanse, the Xindi, the Sphere Builders; with season three, Enterprise set up so many huge things that would later necessarily be dropped simply because they didn't exist in the future. Some of the stories told in the Delphic Expanse were pretty good, but as an overall arc, it just didn't make sense and it left people wondering what happened to the Suliban, the Big Bads introduced in season one's Temporal Cold War concept.
In season four, they brought the Temporal Cold War to an abrupt end. And just like any other time it had been brought up, no explanation was given about what had actually been going on. But other than that, season four was exactly what Enterprise should have been all along. They took the core lore concepts and actually put flesh and bone to what had previously only been a back-story side-note. They even redeemed the Vulcan race from being the stuck-up snobs that we had seen in earlier seasons. This is the expansion that should have been explored since the beginning, but since season four was not season one, it happened to end up being the last one.
Also, the argument that there aren't supposed to be any more ships named "Enterprise" is invalid because there are several navy ships and at least one space shuttle named Enterprise, too. The key is the registry, and the fact that the NX-01 existed before the United Federation of Planets did. The NX-01 belonged to Earth, but the NCC-1701 belonged to the Federation.
Anyway, I know I just made it sound like seasons one through three sucked, but there were enjoyable episodes! If you want to round out your knowledge of Trek canon, it won't kill you to watch Enterprise. Archer grows on you, and by the time he stands in front of a coliseum full of aliens waiting to establish the United Federation of Planets, you can be assured that he finally makes the leap home. [Oh, boy...]