The core of this story reminded me a bit of the film What Dreams May Come, where Robin Williams travels the afterlife to retrieve his suicidal wife from her personal hell. Sorrow blends the Shakespearean lore with Scandinavian mythology, prophetic witches, and lots of swordplay. I don't want to spoil the story, but while it might not have the ending most would want (and it appears this may be the first in a probable series) Sorrow does end on a note of hope. I liked the paranormal twist to the stories and the characterization of the leads. Hamlet is appealingly arrogant, Romeo loyal to a fault, and Juliet is just kickass.
I can't say how Shakespearean purists will like this, but if you're looking for a good young adult fantasy it's worth the read.