Ouch. Emotionally Dense Harry meets Depressively Quiet Severus. Sort of like an immovable object meeting an insensate force. Or fog rolling across a empty polar shore: a gray clammy day becomes slightly grayer and clammier. Poor dumb Harry and mute Severus are stuck, and no one else cares, or can do anything constructive to help them even if they do. A Howler and a heart-to-heart, pretty fitful responses.
It's a compelling depiction, not simply because of the polished writing aimed unswervingly toward their dismal denouement. I'm not sure I know how to appreciate the value of depicting them as so utterly unable to grow and learn anything. Bleh. Not my kind of people *or* characters. However, the story was so well written, I did read all the way through in the hopes of something happening. But rather like in the books, Harry proved consistently unable to mature enough to understand another person, and Snape retained his deep-seated reluctance to try to explain his feelings. (Although I'm not sure I find any satisfaction in the faithfulness to that aspect of canon.) It's like they cancel each other out, and all that's left from start to end is numbness and going through the motions.
Pretty unmitigatedly bleak, all in all, so I suppose that's a solid success on the scale of angst, if not in this reader's mood. :D
*goes off to imagine that first, a companionship of several years duration would have included at least one actually happy moment, and second, that this Harry eventually grows up enough to figure things out.*