Tainted by the Preview: The first several trailers and clips that Marvel released didn't put the animation, writing, and voice acting in a light that fans found promising.
They Wasted a Perfectly Good Plot: Most reviews state that the script seems too juvenile and the animation too shoddy for this movie to appeal to anyone other than the least critical of the youngest Marvel fans. To name but one criticism against the script, after The Avengers, a team up between Iron Man and Hulk sounds like a great opportunity for Tony Stark and Bruce Banner to banter with each other and use science to save the day. This opportunity became wasted due to Hulk never changing back to Bruce in the movie. Under Jeph Loeb, Marvel Animation runs under the assumption that kids find Bruce boring.