ENTERPRISE came out at a lousy time. Coming in the wake of four other Trek series shows and all the movies, the public never seemed all that stuck on the show. Plus, while I was a huge fan, I must admit that the series started slowly---very, very slowly. As a result, the show was canceled prematurely--after the show had greatly improved but lost its audience. It's really a shame.
The series is supposedly a prequel to all the Star Trek shows and shows the earliest journeys of mankind to the stars. I really liked what the writers did with the Vulcans, as in previous Star Trek shows, this race was super-noble. Here, however, they were less angelic--doing their best to keep humans on Earth as well as showing a deviousness that you only slowly came to realize. But perhaps the most interesting race on the series were the Andorians (who were only briefly seen on the original STAR TREK). These arch-rivals of the Vulcans seemed hyper-aggressive and unreasonable through part of the series, but after a while you come to see that the Vulcans really were jerks and dishonest in this series. While the Andorians were not the nicest of people, despite initial appearances, they could be reasonable and even allies. This plot element that was woven throughout the series was particularly effective and I loved how these beings were far more complex than you first thought (much like the Narn were on BABYLON 5).
The major plot running through most episodes involved a doomsday weapon that obliterated Florida when first tested and was destined to be used to wipe out the entire planet and this was an excellent and interesting plot idea. The voyage across unknown space to stop this carnage was kept my interest. Additionally, most of the crew members were interesting and well-written, though since it was made in the 21sst century, they tended to be sex perverts compared to earlier and more chaste series (including one episode where a male crew member got pregnant after making it with another species)! Still, there was a lot to recommend here--too bad it came on the heels of all this other Trek, as it couldn't help but fail due to audience overload.
By the way, there are MANY inconsistencies on the show if you compare it to the original Star Trek, such as the Enterprise looking far more high tech in this series (though it was set in an earlier year). Unless you are a major geek with no life whatsoever, this shouldn't be a major problem. If it IS, then you need to join Star Trek Anonymous!