It sounds like Star Trek NG is the only Star Trek that fully ran its course, withinout being cut short, reaching its full potential.
Lies.
Deep Space Nine and Voyager both ran for seven seasons, the same number of seasons as TNG. And all three had roughly the same number of hour-long episodes (splitting up all of the 2-hour-long episodes of each show in half):
- TNG: 178
- DS9: 176
- VOY: 172
Deep Space Nine had an amazingly impressive series finale that was the grand culmination of so much plot and character development that had been years in the making since the show's very beginning. And it spanned a whopping
TEN episodes vs. TNG's mere two-episode finale.
Similarly, Voyager's two-part finale was also the long-awaited realization of that show's ultimate goal that it had set out to accomplish from the start. It's not perfect, and had room for improvement, but as the show's finale it was adequately serviceable (much like the rest of the show itself).
TNG's finale is great, too, but it's a mostly standalone adventure that didn't have
nearly as much leading up to it narratively, when compared to finales of Deep Space Nine and Voyager that served as a far greater pay off for each to go out on.