I find the show started to decline in quality around season six. Most of the decline in quality had to with behind the scenes issues and over stretching of resources. In season 6 most of the writers attention was on launching DS9 certainly Michael Piller had no direct involvement with TNG after season 5. Then in season 7 the producers and writers were: writing the second year of DS9, prepping Voyager and working on Generations.
I agree with the sentiment expressed by some about Generations coming too close after the end of TNG, but that was a studio mandate. They wanted to strike while the iron was hot so it was decided filming Generations would happen right after the end of the series.
That said, Seasons six and seven did have some great stuff and some good character development (minus Beverly having sex with a lamp)