I'm not a big comic reader, so this statement doesn't necessarily carry much weight, but this GN is easily the most impressive use of the medium I have ever seen. Twelve years in the making, you say? Totally worth it, and yet you'd never know just by looking at it. That's what excellence is, I suppose: Making great feats look completely natural, easy almost (at least to untrained eyes).
The ending was certainly shocking, but I found it to be... well, not uplifting, but really hopeful in a way. It's a fairytale ending, with death by comet replacing the happily ever after. Asterios reaches his destination, spiritually and physically - by killing him and Hana off at that point, the blissful purity of the moment is preserved, without the possibility that the reality of the characters' situation, their baggage as a couple and as individuals drives them apart again.
Of course, that reading feels kind of unfair to Hana as a character, as she only serves to make Asterios whole and is then killed, but then again, the book never tries to disguise the fact that the story really isn't about her.