I think the love of the ST series is also dependent on when you saw them. I saw TOS in reruns as a kid and loved it (actually, I know I saw at least part of one episode in its original airing, but I was only about 3 years old). When TNG came out, I was almost done with college. When TNG was on, it was the ONLY notable SF on TV, and it was syndicated, so not everyone got to see it. At the time, we were so excited to see NEW ST on TV, watching it became a ritual. DS9 came on before TNG ended and it was also good, and was also syndicated. Voyager came on before DS9 ended, but it was on a network, so it had a more regular time slot. However, by the time it arrived, some of the trappings were getting old. Spock was such a strong character (the emotionless alien showing us what being human meant) that they copied him in every series - Data, Odo, Tuvok/7 of 9...Trulane became Q... etc...
TNG tried to be a better version of TOS. I think in many ways it succeeded because it had way more money (in later seasons) and let's face it - better actors.
DS9 just tried to be different by being on a station.
Voyager just tried to be different by taking the federation away. IMHO, they started out well, but went downhill quickly after the first season.
I have seen very little of Enterprise, so I won't comment on it.
One thing all the series except TOS and TNG did that I think was a mistake, was to make them more serialized.
B5 was serialized and brilliant because JMS knew where the whole story went before he started the first episode. The later TS series weren't really like that. They had an implied order but it never looked liked the writers knew what they were going to do next season as a result of what was going on this season.
I am one of the people who learned to hate voyager. The reason is that it started out well, with a good premise. It had a group of very interesting characters (ok neelix was annoying at times), but around the end of the first full season, the plots started to get really dumb. I remember watching every episode, really loving it at first, then watching it go downhill until the "warp 10" episode (where the two characters go off and become lizards and have babies) and then thinking "Well, that's enough for me." Once in while I would see it flipping channels and wonder if it ever got any better and ever time I'd watch a few minutes and decide that it hadn't. I did sit and watch the whole finale and it seemed just as dumb and full of plot holes as most of the show had been. I guess what makes me bitter is thinking how good the show *could* have been.