I'm shocked that its been 20 years! I can remember watching the first episode with my family. I was 10 when it came on and at the time I was a huge TNG fan. I think like a lot of fans I didn't give DS9 a chance in the early years. I don't remember watching it beyond the first episode. Once TNG went off the air I started watching DS9 mainly because I didn't want to miss my weekly hit of Trek. I started to like it but it wasn't until Way of the Warrior aired that I really fell for the show.
DS9 was and is my favorite of the Trek spin-offs. One of the reasons I love the show so much is the fact that at the end of the day it's about character. These characters grew and were fleshed out during 7 seasons and never under utilized. The writers took chances and not every episode had the happy 'everything is wrapped up in a bow' ending that the other spin-offs seemed to do often.
I still think 20 years since it first aired, DS9 doesn't get the respect it deserves. If TNG brought sci-fi into the mainstream for much of the 90s, I think DS9 played a big role in the change towards the more complex character-arc based sci-fi of today.
It also makes me sad that it's very hard to find DS9 reruns on TV these days. Here in Canada, it's still pretty easy to find TOS, TNG and VOY but DS9 hasn't been rerun in a long time. I'm hoping the show does eventually make it to blu ray and allow a new generation of fans to get hooked!