I can see why the stories deteriorated and the writers and producers seemed to lose interest.
They were so caught up in playing safe (not necessarily killing off main cast) so as not to upset a few oversensitive hard core fans they cornered themselves in a box.
If the Writers were allowed of there leash abit they may have been able to keep the franchise fresh.
Instead we get TNG 2:00 and with ENT TNG 3:00. At least ENT came into its own on series 4.
Thats the problem each series should have its own direction and personality.
Its why DS9 and TNG have so much staying power 20 years later.