The problem for me with DS9 was the way it changed from the tried and tested one or two episodes per storyline to a long running epic tale.
Now that's all very well if you can be sure to watch the whole run of the series, but I usually find that I watch the first few then something prevents me from seeing a couple and then I've completely lost the thread of what's going on.
X files did the same. The first few episodes were self contained, then the bigger storyline came in and I lost interest.

As for Voyager, is it just me that finds Janeway incredibly irritating? (it might be because she really reminds me of my first mother in law I suppose)