DS9 is the only series I can think of that actually had a solid final season and pulled together a series worth of pieces together in a smart satisfying way--where even if it was done on the fly it made sense ultimately in how it all came together.
I can think of one other show, and that's the one that DS9 was always compared to - Babylon 5. Both had great arcs with an apparent end in mind, and the execution of the larger percentage of their episodes was top-notch. I'd rank both shows in my top five.
I definitely agree with you about Babylon 5 - that show was fantastic. Though I never watched it when i was younger I got into it about a year ago and watched the entire thing, absolutely fantastic storytelling. I haven't watched DS9 in its entirety, but from what I have seen it is some great storytelling, and I did enjoy the finale.
Though Voyager will always be my favourite Trek series I can understand why people say that it left threads hanging, because the television series did. I read the novels that take place post-Endgame and I feel like a lot of those threads were tied up there.
But back to Fringe, I'm just hoping that this final season is enough to wrap Fringe up properly so that there are no loose ends (like I mentioned with the Voyager finale).