Was moving TNG to the big screen a bad decision?
I would say no, but I do think that the move was rushed, especially in the case of Star Trek Generations - review here:
I'd also contend that ST:TNG never really had a proper movie on the big screen! TNG was an ensemble peice, unlike TOS, which had the big 3 characters. I think that it needed a writer and director that appreciated this - someone like Jos Whedon, whose Serenity movie and Avengers film both catered for the ensemble casts.