I loved TOS. As a teenager, I collected all 79 episodes onto VHS tapes in sequence, since it was on in syndication at like 2 am 5 days a week. Even when it was bad, it was fun to watch.
I didn't want to like TNG. I resisted watching, but the buzz was good about it (even in those pre-Internet days). Once I started, I found I liked it. It wasn't TOS. It was good, but in a different way. When TNG is bad, it is also dull, and I watch the clock. But when it is good, it is great. I like the ensemble cast (I didn't love all the characters, but I didn't hate any either). I like the feel of the show for the most part. I agree with Warped9, though--season 6 was hugely variable in quality, and season 7 was awful. I was very disappointed in the TNG movies, since I liked the TOS ones (except for ST V).
I didn't like DS9. I didn't like the soap opera feel to it, I found Sisko to be dull, the Ferengi to be stupid, and Bashir to be annoying (to watch, I think he was probably supposed to be an annoying character). I did kinda like the episode when Tom Riker steals the Defiant. It could have been interesting if they brought him back as a recurring character. I like the idea of seeing the road not traveled with Starfleet's poster boy.
I really WANTED to like VOY. I actually thought the premise was really interesting, but the characters were so dull. The episodes had no life. And I couldn't stand to watch Neelix at all.
I haven't watched even a single episode of ENT. I hated the premise, and the execution doesn't sound like it was good either.
I kind of don't understand all this arguing about "giving things a chance". There is plenty of room for reasonable people to disagree about whether entertainment works for them. I find my own opinion closer to Warped9 and BillJ than RAMA, especially about so-called top-10 episodes like The Inner Light and Tapestry (hated them both, and could barely sit though my one and only viewing).