What made Insurrection fail was that the villians were 2-dimensional. They were shown as evil since they dealt with banned weapon systems. It also wasn't clear why were they sick and what had caused it. Were the Sona their own race and how did they build up their own fleet after being kicked out of "Eden"? Also the CGI on the Ent-E didn't look as good as the model did in FC. By Nemesis even the Bridge looked cheesy. In FC the Bridge looked great.
My feelings are that Insurrection didn't kill TNG trek. The mistakes done after the series ended was coming out with Generations right after the series ended. It felt like a souped up TV episode with Bipolar uniforms. I believe that they should have waited until FC to come out with their first feature film. having the Ent-D destroyed by the Borg would have justified Picard's behavior in FC (especially his speech to Lilly about not wanting to loose the Enterprise again). In the end there was TNG fatigue with the movies not doing justice for the series. The movies were just not at the epic level of Star Wars.