I can understand some fans liking one series or another better than the others, but I cannot fathom how a true Trek fan can say they do not like one or more of the shows AT ALL. What is it about Star Trek that one really likes, which makes them watch it again and again? It cannot be the characters alone, because there are different ones in each show. It cannot just be the aliens, because while there are commonalities, there are some aliens that only appear in one series. It has to be the universe, the common themes, the space exploration, the whole concept that we are destined to travel to space and explore the unknown. And all of the series have that - which is why, for one, love them all.
Now, as to the question at hand, what about Enterprise? Like Commander Willow above, I was a latecomer, not having watched it during its original run. But then I watched it on DVD and am now watching some of the episodes on Netflix and I have to say that it is really quite a good show. The stories are interesting, the aliens captivating, and the integration into the Star Trek mythology works very well. One thing I am thankful for when I watch Enterprise is how we learn in depth about aliens that we never did in the other series, such as the Andorians and Tellarites. I also enjoyed the Xindi story arc and thought the extended stories in season 4 were great as well.
All in all, Enterprise was a great addition to the Star Trek universe and I, for one, think that it will stand the test of time.