Prior to the episode's release, many were apprehensive about how the Marvel characters would be characterized. After the special aired, it turned out that it was the characterization of Phineas that was most divisive.
Unconventional Learning Experience: Though Candace pointing out that energy can never be destroyed is based on her reading of comic books, the rule also applies to real world physics, which children watching this show may not necessarily be familiar with.
They Wasted a Perfectly Good Plot: Many people feel that Isabella's issues that made her feel useless should've been elaborated on more outside of her song with Candace.
The Woobie: As always, Candace, who can't help but screw things up every time she tries to help (until the end of the episode), to the point where the normally cheerful Phineas yells at her several times and revokes her S.H.E.D. membership. She even sings a sad song about her predicament alongside Isabella.