It was a big mistake not to allow Bruce Timm to do the animation. He gets the Universe better than anyone.
" Timm was the co-creator and producer of Batman: The Animated Series, which premiered in September 1992, and went on to co-create and produce Superman: The Animated Series, The New Batman Adventures, and Batman Beyond. He also served as producer on the feature-length Batman Beyond: Return of the Joker before taking the helm as creator and producer of the animated version of Justice League, this series continued in the form of Justice League Unlimited. Timm was also the executive producer of the Teen Titans animated series. "
These were some of best cartoons/animation ever made.
I think Gunn will do fine the with film division, he get's comics and can balance story with humor and drama.