For me, it's that several units are very fledged out (Tangled, Peter Pan, Maleficent, Pinocchio/Dumbo), but a few don't seem quite complete (Little Mermaid and Brave). Both lack the level of energy and interactivity of the other units, Brave more so than Little Mermaid.
Little Mermaid's problem is an easier fix of adding more dancers and choreography (though a thought did spring into my head that a daytime version of SpectroMagic's Ursula would be a great addition, but that's a bit more conceptual). Brave's issue is more float based. Compared to the moving elements in the other floats, it is easily the most boring float in FOF. Which is a shame, because it has a really unique float design, and in concept, I loved it. If there were props/smaller units surrounding the float with kinetic elements, I think the static nature of the Brave float wouldn't be an issue. Neither unit is in any way bad by itself, but combined with the rest of the units, they need more than what is currently there.