Wow. There were plot holds big enough for a dinosaur skeleton to walk through, the human characters were just so painfully stupid and generally outright awful people, and nothing in the plot made sense... Yet all the museum characters sort of semi-saved the movie. It was great seeing them again, and I've always loved the idea of things coming to life at night.
Through the movie, I kept saying "Well, maybe the next one will be better". This is the third one, and it made a good deal of profit, so there'd be a fourth one, right? Wrong! Sadly they're stopping at three! Arg! So it made all the goodbye scenes with the characters feel all the sadder.
Adding to the sorrow was that this was Robin Williams's last movie, and he just seemed so happy, loving, and enjoying life in it. And the scene where his character was saying goodbye? So hard to watch. I'm getting choked up now just typing this and thinking about it.
I wish this had been a much better movie, for many reasons. There's room in the plot for a Night at the Museum 4 if they change their mind. I really hope they do.