I've been watching Voyager recently (I only caught a few episodes while it was on the air), and aside from bringing up aliens they met in previous episodes, each episode seems pretty "bottled". Enterprise (Seasons 1 and 2) had a flow to episodes that put them into a framework, but Voyager seems like you could just shuffle the order the episodes occurred in, and you wouldn't lose anything. (As a big fan of TOS, I am going to completely ignore the fact that it was largely the same. Voyager had a big, long, semi-plot of getting back home, and Enterprise had humanity's first voyages into a large galaxy. Enterprise seemed to hold to the premise better, IMO.) I think Enterprise benefited from its premise of "we're making up the rules as we go along and encounter things we never thought of" to show the beginnings of the Prime Directive and other concepts. Voyager seems to throw them out the window and have the characters either hold the Federation rules as sacrosanct or considered an irrelevant obstacle to be discarded as the plot demands.
I largely agree with this. I think season 4 was building to something beyond, but the series got canceled before it could have a payoff. All the time-travel crap could have been done away with, though. And that series finale was a disgrace.
DS9? I tried to watch it. It bored the hell out of me for several reasons. I am also opposed to a Star Trek series set on a space station. The idea was to boldly go, explore new worlds, and meet new people. Not to boldly sit here at the same location and wait for the same repetitive people to show up to the same already explored place. It's Star Trek, not Star Sit Here.