You obviously are a devotee, and one respects that, while at the same time wishing you had talked as much about the film as you do about the band and your personal history in relationship to it.
Ian Curtis is significant because he was a great songwriter, evocative singer, and a member of a band that was a vital, creative force in modern music.
Yeah, I guess so, but how do we know that? The movie doesn't really make these things clear either--or show how Curtis became who he became. It's not easy to do that, and this is where the film draws a blank for us.
A great deal of effort has evidently been spent in recreating the live musical performances that made such an impression on Cobijn. Sam Riley probably spent countless hours studying Curtis' singing and stage mannerisms in order to create a facsimile_however the shortened length of the show numbers indicates insufficient trust in their power to engage the non-fans in the audience.
Though you find the performance sequences too short, you do acknowledge, I guess, that they are riveting, though you say that only by commenting that a lot of research went into recreating the music. Probably the shortness of the performances was not due to any assessment of the audience's level of patience but the desire to achieve artistic economy. That said, I admit I like sustained perrormances myself, and this is one of the things I dislike about TV music documentaries--they're too choppy. So I can sympathize with you, while also seeing Corbijn's desire to avoid a sprawling work.

This is where Control excels: it feels like a slice of life, a piece of the time and place, and not a biopic. It may leave a lot out for the admirer of Joy Division, but by limiting its focus it achieves particularity and freshness. Sam Riley, whose performance you say nothing personal about, is also striking looking and charismatic, very effective in the role of Ian. Did you respond to him?

P.s. "UM" could be "University of Montana," "University of Michigan," "University of Missouri," etc. Evidently you mean the University of Miami?