Why did the Batman series fall apart so quickly after the 1989 movie?
What I mean is, Batman Returns seems to be one of those "you either love it or hate it" type of superhero movies. It was definitely very controversial when it was first out, with parents complaining about how dark, violent, and overtly vulgar and sexual it was compared to the 1989 movie. To add insult to injury, McDonald's had to cancel their Happy Meal tie-in due to all of the controversy.
Batman Forever is really a soft-reboot of the franchise after the first two involving Tim Burton, Michael Keaton, and Danny Elfman. It was clearly meant to steer the franchise in a safer, more marketable territory. Batman Forever is quite frankly, a movie that you could say while not exactly "good", it wasn't at all horrible either. It was really a bridge between the darkness of the two Burton movies and the cheesiness and bright and colorful campiness of Batman & Robin.
What else is there to say about Batman & Robin, other than it killed the franchise until Christopher Nolan got his own trilogy of Batman movies going eight years later? It quite possibly could've killed the superhero movie genre for good until X-Men and Spider-Man (and to a lesser extent, Blade, but I wouldn't exactly consider Blade to be an out and out superhero movie) got it back on track about five years later.