Uma Thurman kills in this movie. She's like if Lady Gaga were a Batman villain. I'll just quote the Comics Alliance review of the film:

Chris: Clooney has joked about this movie a lot -- when he was nominated for the Oscar for Michael Clayton, I remember him telling reporters that he was there to pick up his Lifetime Achievement for Batman & Robin -- but he's actually pretty solid in the role. He does a more convincing Bruce Wayne than anyone else. My real high point, though, is Poison Ivy.

Chris: You talked a lot about Jim Carrey attempting to channel Frank Gorshin as the Riddler in Forever, but while I think that's a pretty miserable failure, Uma Thurman is way more successful at trying to be Julie Newmar.

David: She does a great job doing the campy sex-vamp thing. A GREAT job.

Chris: Ivy's better written than Freeze, in that she doesn't have a constant string of puns, and Thurman's delivery is perfect for the material, right down to her faux-sultry Mae West voice.
Clooney in my opinion shares a problem with all the pre-Bale Batmen - he doesn't really know what to do with himself in the dual role and only really sells Bruce Wayne. Michael Keaton had the same problem, and Val Kilmer doesn't really work in either sense. As for Thurman I thought her performance was great. As for how much time her plot had to develop, don't you think that's kind of beside the point? At one point she invades a social gathering dressed as a giant gorilla and then prostitutes herself out using her pheromones. I'm not really worried about her character arc that much.