I want to start by explaining my history with Star Trek and where Enterprise fits into it.
I was born during the run of the original series, though being only one year old when it was cancelled I really don't remember if I was ever put in front of the TV while it was on. I did however watch it in syndication while I was growing up and though I liked it Star Trek TOS (the Original Series) wasn't an important show to me. If it was on and I came across it I watched it but I didn't go out of my way to find it. What really launched (pun intended) my love for Star Trek was The Next Generation. I started watching with the premier and watched every episode for it for it's entire run. The Next Generation was the first TV show that I cared enough about watching that I didn't want to miss a single episode. I enjoyed The Next Generation so much that when Deep Space 9 and Voyager premiered I started watching those series immediately though they never really clicked with me. They were good enough but as I soon discovered while continuing to watch both TOS and TNG (The Next Generation) I really liked the exploration and discovery, the first contact and wonder of Star Trek the most. DS9 (Deep Space 9) was a show about a mostly stationary Space Station and Voyager was a show about a displaced starship trying to get home. Neither show spent much time with the aspects of Trek that meant the most to me and when they were on TV originally I didn't finish watching either series. In fact, I don't think I finished the first season of Voyager and I never made it past the second season of DS9. The reason I tell you this is because the next Star Trek series on TV was Enterprise. It started the season after Voyager ended and I have to be honest I didn't watch a single episode when Enterprise was in it's first run mostly due to the disappointment of DS9 and Voyager. Looking back now I couldn't have been more wrong.
As Enterprise went into it's third season a couple people I know mentioned to me how much they liked it and asked if I watched it. When I told them I didn't they said I should give it a try. I didn't. To compound my error in not watching it originally I thought that if people who were not Star Trek fans already thought it was good it probably wasn't good Star Trek. Yes, I know stupid, stupid, stupid.
After the series ended it's run and was released on DVD the planets aligned and put it squarely in my path. TV at the time was, for me at least, a wasteland with only a few oasis to keep me going (The West Wing which was in its last season, Battlestar Galactica, and Deadwood). By the time Enterprise showed up on Netflix for rental it had been long enough since the Voyager and DS9 disappointment that I actually wanted new Star Trek to watch. Enterprise surprised and delighted me with great stories and a series based on exploration and discovery. Enterprise was everything I was looking for in a Star Trek Series.
Enterprise was so good that I increased my Netflix subscription to 3 discs at a time just so I could watch without interruption. Those of you who have a Netflix account know what I mean, with a 3 day turn around it takes 3 discs at a time to keep one unwatched disc at home constantly with one on its way out and one on its way back in. I burned through the series fast watching an entire disc in one day many times.
Which brings me finally to the series itself. I enjoyed the first two seasons immensely, the combination of watching the early years of Starfleet with the first contact of so many races that became (already were?) staples of the Star Trek universe made for a great show. Enterprise had the magic that had been missing from the last couple series. The production was great as well and I think Broken Bow is the only pilot episode of any series that I like as much as any show during it's run. Even TNG had a weak pilot and the entire first season showed growing pains but Enterprise was different. While the characters still developed over the series run and the actors did become more comfortable in those roles I never got the feeling that the crew was "new". From the first episode to the last Enterprise was consistently well written, well acted and well produced. Even the episodes I hate I have to admit were well done.
The last episode of season 2 started what I consider to be the worst story arc in Star Trek History. I hate the Xindi story arc altogether and the entire third season for me was a chore to get through. Gone was the exploration, the discovery, the pure joy of being the first humans to experience everything they did. It was all replaced by bigger weapons, Space Marines (MACO's), a hunt for revenge, and a number of characters making 180 degree changes in attitude and motivation. Especially painful to me was Captain Archer losing his moral compass completely and becoming a "do whatever is necessary to stop the Xindi" character. To me this was not Star Trek, never mind the fact that they changed the title from Enterprise to Star Trek: Enterprise for season 3, it still wasn't Star Trek, well I guess it is if your J.J. Abrams but that's a post for another time.
Season four thankfully ended the Xindi arc though trying to recover from it would prove difficult. In the first two episodes they end both the Xindi arc and the Temporal War arc oddly enough while tying them together. The rest of the season is spent trying to find the balance they had in the first two seasons. There were some bright spots and season four was much better than season three. I especially liked the Dr. Arik Soong episodes and how it pointed in the direction of Data from TNG, I liked the introduction to the Tellarites another TOS race we meet again for the first time.
They even managed a couple mirror universe episodes and everyone likes mirror universe episodes, well maybe not everyone but I do. Too much of season four is spent defending Earth and investigating terrorist attacks and threats to really get back to what I liked most about Enterprise. The series finale has gotten a lot of bad press and I don't think it deserved most of it. Yes, turning the last ever Enterprise episode into a TNG episode was a bad idea. I would have liked to see the same ending but told as an Enterprise episode and not as a holodeck program on TNG. The thing is though, at least we got a finale. How many TV series have ended simply by being cancelled and left you with no ending at all or worse yet only the first half of a well done cliff-hanger. I still think Enterprise would have done well if given another season to regain control of the plot and characters maybe even making it past the seven seasons TNG ran. The first two seasons of Enterprise are to me the best Star Trek ever on TV. I still like TNG as a series better but I will put the first two seasons of Enterprise up against any two seasons of TNG you want to name.
If you have never watched Enterprise then I can strongly recommend it no matter what anyone else says you will enjoy it. If you have seen it, do a re-watch like I am. You can watch it streamed or rent the DVD's from Netflix and Amazon Prime Instant Video. Alternately you can purchase the series on DVD and on Blu-ray (about freaking time) where season one is now available.