"Look at all the famous people we got to play Bob Dylan" is an unabashed gimmick. It works because of how fragmented Dylan's life was, and also because the road movie, the western, the domestic drama, the Pennebacker/Fellini head trip, the come-to-Jesus rockumentary, and the single-shot confessional are all self-sustaining and distinct. The flaw is that they don't always cut together well (but most of the time they do, which is crazy).
And honestly, it's a blast watching all these talented folks do Dylan. Blanchett is probably the most impressive because it's the most transformative performance, but on this viewing I really appreciated the laser accuracy of Ben Whishaw's piece. I tend to like Dylan covers more than straight up Dylan, and I'm Not There. is one big Dylan cover mash-up full of poetry, emotion, and ambition.