I'm watching the Shadows of the Bat BtS documentary for Batman and Robin right now, and, to be perfectly honest, Poison Ivy and Mr. Freeze really aren't what's wrong with the movie; there's actually a good story in there with regards to their characters, and Freeze in particular isn't any more OTT than The Joker, The Penguin, The Riddler, and Two-Face.
The problem with the movie is that, at some point, George Clooney decided he didn't care about the project and, instead of leaving (which is honestly what he should've done, even though they were in production already), decided to do everything he could to intentionally shit on the Batman character, which in turn got Chris O'Donnell to intentionally shit on his character, which in turn made it impossible to take the story and the villains seriously.
There's actually the core of a good movie buried in Batman and Robin; it just gets strangled by the poor acting decisions of George Clooney and Chris O'Donnell, which was then exacerbated by Joel Schumacher's decision to focus the second time around on the more outrageous and lighthearted aspects of the film being a live-action comic book, creating a scenario in which any level of respect for the characters and the comics just got suffocated.