What a great story! Your young Snape was fantastic. I loved how you took his canon character and his background and added to it, fleshing him out even more, giving him even more depth and layers. Oh, how my heart ached for him. Really fantastic characterisation. And Harry, too! I loved him from Snape's POV, from his own POV - he was just wonderful. And the plot, and the way you twisted canon, while still keeping the story canon-compliant, was brilliant.
One of my (many) favourite moments was the hint that Dumbledore helped Snape survive despite his insistence that Harry should not alter the future in any way.
Oh, and your writing! So much love. Like, your use of parentheses - I think I have a thing for parentheses when they're used that well. *g* But everything about your writing was so engaging, it was such a pleasure to read.