Bah, I already wrote another long post about this, but decided to simply "summarize" it to the following.
It just starts to feel like an overused gimmick in many cases, in lack of something else interesting to tell a story about. Treks seem to be among the worst "offenders" as far as time travel goes. For comparison, Babylon 5 had an important role for time travel in the form of Babylon 4/Sinclair/Valen, but it wasn't overused. Similarly Farscape had a bit of time travel, but without going overboard. Thankfully Galactica had none (that I can recall, anyway).
Now, this is of course just my personal view. But if you have to mess with the established timeline in rather serious ways to keep things interesting... well, I wouldn't call that an optimal situation in my books. That's not to say there aren't time travel episodes that I like, there are in fact several. But ones that alter events already shown in the series (or in case of Trek, also in the other series) previously often feel kind of lame. And the same thing with something like the time travel in Endgame.
It just starts to feel like an overused gimmick in many cases, in lack of something else interesting to tell a story about. Treks seem to be among the worst "offenders" as far as time travel goes. For comparison, Babylon 5 had an important role for time travel in the form of Babylon 4/Sinclair/Valen, but it wasn't overused. Similarly Farscape had a bit of time travel, but without going overboard. Thankfully Galactica had none (that I can recall, anyway).
Now, this is of course just my personal view. But if you have to mess with the established timeline in rather serious ways to keep things interesting... well, I wouldn't call that an optimal situation in my books. That's not to say there aren't time travel episodes that I like, there are in fact several. But ones that alter events already shown in the series (or in case of Trek, also in the other series) previously often feel kind of lame. And the same thing with something like the time travel in Endgame.
