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We know relatively little about Marie, but it almost feels like she has a growing presence as the film proceeds. As you grow to observe Charles and the way he interacts with the world, you try to picture the sort of woman that would have fallen for him (and he for her). You wonder what were they like as a couple? Is his inability to stop speaking something he acquired after her death or something he did with her as well.
I also enjoyed the way that the movie walked with you through Herb's eyes, as we grew to see the underlayer of Charles as a character. What starts as a seemingly unhinged super fan becomes something more as you realize that "McGwyer Mortimer" is not just a group that he loves, but a deep connection to his deceased wife.
I especially like the scene were Herb basically watches the sunset with Charles just blathering by his side. Eventually reaching a sort of Zen moment where he recognizes that a world with Herb "ruining" a beautiful sunset is less desirable than one where he gets to fully experience the sunset alone. Not everything in life needs to be met on your own terms.