I disagree, well I half disagree sort of. First Contact is the best of anything TNG, and also the best Trek film - my opinion there will never change. Generations gives them a run for their money but I would more than likely say it's better than the two-parters but it really depends what I'm in the mood for. Insurrection and Nemesis were about on par with TNG standard.
So to answer your bias question why did they drop the ball...they didn't. They could've done better but they didn't really do worse.