The problem with any "Star Trek" is that you have to keep the fresh material coming, which in a space show, generally means you have to keep fresh aliens coming. People don't seem to remember that the original series pretty much popped out a new alien civilization a week, many of them comfortably in the "Q" range of advancement. At some point, continuity would have frozen the series solid, if they had paid close attention to continuity.

The history of TOS was quietly shoved off the table for later series. "Organian Treaty? Never heard of it." And what happened to all those different planets they found with enormously advanced god-like species?

More skilled writers could have expanded on some of this. "The Wrath of Kahn" wasn't a bad revisiting of a TOS episode. I could think of a lot of things that could have been done in "Next Generation" along those lines.

As for "Enterprise," it had a promising start, dealing with Earth chafing under their treatment as a "client species" by a Vulcan culture still not quite at the maturity stage of Spock's time. A lot of work could have been done with this. The political interaction with the Andorians worked pretty well, too. Some individual episodes touched some nice places, like the slow freighter culture and others.

The writers got lazy, and pretty soon the transporter was back on line, and we were even seeing signs of holodecks and other tech that wasn't anywhere in sight in Kirk's time, not to mention aliens that somehow the Federation of Kirk's time knew nothing about.

Okay, maybe "lazy" is a little harsh. By definition, anything the slow-moving Enterprise NX discovered would have to be old news to the TOS, never mind Next Generation era. It's not easy to find new ideas under those circumstances, and explain why they never showed up in later series.

Of course, time travel is the kiss of death, but the Star Trek producers seem to be inevitably drawn into it.