DS9 was interesting because it was the first series that took place aboard an alien vessel, not a Federation one. So the rule book had to be adapted, and -with all the aliens dropping in - it made for exciting possibilities. Though the Dominion War did drag on too long.
Voyager was OK, never really liked Janeway and how she hammered home the prime directive all the time then disregarded it when it suited her. And how they ended the series was a real let down. Too quick, too neat, nothing about the crew re-acclimating to earth life. The final episode or two should have been about how all of the crew were adjusting to home life.
Enterprise had such potential - a clean slate to do all sorts of things and fill in the blank century between ST: First Contact and TOS. All they had to do was make sure they didn't get too far out of what was to follow. Instead they dithered with recycled stories, and the two big story lines (Xindi and the Temporal Cold War) are never mentioned afterwards. You'd think that things that big would have been mentioned later on. Though they did have that Borg connection and the thing with the Tholians and the USS Defiant (Connecting to "The Tholian Web" TOS).
My biggest complaint with
DS9 was their heel-face-turn to come up with the Dominion War in the first place. You'd think that with their early visits to the Gamma Quadrant, they'd have figured out that the wormhole was dumping them off in the middle of another star nation, or that the Federation would have instantly assumed that this was happening, fast-tracked the Bajorans into the Federation, and reaffirmed its alliances with adjacent groups like the Klingons and worked to make peace with the Cardassians. If the Dominion War had been conceived-of with the series, there would have been talk of its existence before it was met head-on, possibly even by a couple of seasons. It could have been a bogeyman equivalent to how the Borg was for
TNG.
But then, over the last several years I've been big into David Weber's
Honor Harrington series, which features wormholes and their exploitation for both commercial and military use, including when two adversaries control opposite ends of a wormhole. In that scenario, basically both sides go crazy with militarization, ready to destroy anything that comes through on almost a hair-trigger, and ideally, one entity has the forces to control both sides of a wormhole, even if the far-side's radius of control is limited something short like a light-minute.
I wasn't thrilled with
Voyager's end either, but in some ways the abruptness actually made sense. Long, slow, arguably boring history is punctuated by important events that fundamentally change things. Perry's sailing into Tokyo Harbor to force Japan to open to trade. The assassination of Archduke Ferdinand by Gavrilo Princip that led to WWI. Germany's roll into the Sudetenland. The two nuclear bombings that led to the surrender of Japan, all fundamental changes that happened quickly amidst the otherwise slow-burn that is human history. They didn't cover the psychological effects of the return of the crew to the Federation, but I'm not sure how they could have done that without it being, well, kind of boring to watch. After all, neither Picard's post-Borg storyline nor Sisko's post-Wolf-359 storyline were especially popular with the audience, and that was even having time to continue back to normal stories.
I did realize something else though, back on
Star Wars vs.
Star Trek that is important. In
Star Wars they're way, WAY too cavalier about the destruction of planets. Planets are valuable, they're places to live that don't require vast amounts of labor and machinery to maintain livable. Destroying planets themselves is extremely foolhardy. Sure, wiping-out the existing population might in-universe make sense, but the ecosystem and the rock itself has huge value as a place to have one's population live. Destroying that is extremely foolish and short-sighted.
