The problem is that they never managed to make their time travel stories the least bit interesting. "Future's End" which is not as bad as the others is filled with pure nonsense.
The mobile emitter? I mean the idea that they could just use an advanced piece of technology of 400 years in the future without anyone from that future noticing any changes is just stupid!! Don't you think that if someone went back to say the 15th century and taught them how to do cars it would change history a little?
Nonsense!
And what is the standard here? Future's End is actually Voyager's
only typical, traditional, sci fi time travel story, as in- The crew go back in time, to our present or past, where we will see them in settings familiar to us, to save their future.
And the genre/style used in the episode episod is "fun action/adventure." What can we compare it to in Star Trek?
There's TNG's "Time's Arrow," with Mark Twain, also an action/adventure but maybe slightly more serious.
Most of TOS's time travel episodes: There's
Tomorrow is Yesterday, where the pick up an air force pilot in the 1960's. There's
Assignment: Earth, which is similar; fun action/adventure and traditional type of time travel story. And lastly, there is
The City on the Edge of Forever, but while this one is a traditional T.T. story, it is more serious, a drama and a romance.
How about DS9? They did
Past Tense, which is more of a serious drama, but traditional nonetheless, and a plot hole greater than any you might find in Future's End. Then there's
Little Green Men, a Ferengi Comedy(which is one of my ffavorites, but certainly not made to be plausible, or taken seriously). Then there's
Trials & Tribble-ations, which is borderline a traditional time travel story, and is not meant to be taken seriously.
How else did Voyager use Time Travel? I would argue they almost always found a new way to make time travel more interesting, and handled it much better than TNG & DS9.
We have a few semi-time travel stories in the first season. in
Parallax, they see a reflection of themselves from an hour or so earlier.
In
Time and Again, they come upon a recently destroyed civilization, beam down, and later realize
they destroyed the world a day earlier. This is good sci fi.
Then there's
Eye of the Needle, where the crew find a wormhole going back near federation space. They communicate with someone on the other side, but later realize they were talking to people 20 years in the past. It's a fantastic early episode. DS9 tried to this in season 6 with
The Sound of Her Voice and failed, imo.
Next up is
Before & After, where Kes is experiencing history in reverse, and begins as an old woman because of a treatment the doctor tried to extend her life with.
None of these were interesting? And the best are yet to come.
There's
Year of Hell, which is a pretty universal favorite of even non Voyager fans, and like some of the others is total a novel take on time travel.
After that is
Timeless, another fan favorite, an interesting take, and very well written.
Next is
Relativity, a follow up to Future's End, and likewise a fun action/adventure story, and maybe a bit of a thriller It involves the timecops, and we get to see their ship and what what they do.
Then there's
Fury, which a lot of people don't care for, but not because it isn't a novel or interesting idea in regards to time travel, and it still has its moments, like Tuvok getting confused and suspicious.
After that is
Shattered, which is basically Voyager's very original and interesting version of a clip show, but not a clip show. It's a lighthearted romp through Voyager's past seven years.
Lastly is
Endgame, which is essentially like Timeless, but not as good.
Most of these are excellent, and original to Trek, which is saying a lot since Voyager was the fourth series and hand to find ways of being creative when hundreds of Trek episodes had already been made. Even Voyager's borderline "time anomoly" episodes are very good, like
Gravity, and
Blink of an Eye.
I would say the best time travel episodes of TNG and DS9 are Cause & Effect, Tapestry & All Good Things(which are simply Q causing the time travel), The Visitor, and maybe Trials and Little Green Men(the last two dont do anything interesting with time travel, but are good for other reasons). Voyager definitely did more iinteresting, or at the very least, as interesting things with time travel as their predecessors.