Though it does provide explanations for the way things work, in many ways, the most important contribution of UC is the questions it raises. More than anything, McCloud excellently points out that we should be thinking about certain things. Why is it that we can understand sequences of images? Do we have receptive differences when engaging cartoony versus realistic drawings? Not many people were thinking about these issues at that time (including the Europeans, though they might claim otherwise).
Quite astutely, McCloud does acknowledge that the understanding for most of these things happens in the mind, though he doesn’t fully probe what that means. More than anything, he’s raising the questions and pointing to a place for the answer.
Rather than my harsh critique calling Closure essentially a rhetorical trick of a faux cognitive process, instead, it might be considered a placeholder for a more developed theory. Yes, McCloud doesn’t really identify what the mind does to connect panels, but he does recognize that the mind needs to do something in order for understanding to take place. So, we can call “closure” might more positively be framed as “details to be named later.”
As much as I may pound away at the theories in Understanding Comics, the only reason I can do so is because I obsessed over it when I was younger. And, when you pour over something that much, you’re views might change as you start applying and pondering it more. It really is a great foundation. Though foundations are meant to be built on… or sometimes bulldozed in order to build something better…