I should be ashamed of how many times I have reread it.. when I could have pursued new, shiny and excellent Snarry.
But here it is, why I choose it - it is what I want from Snarry, most of the time: Snape who is hero but not the sacrificing himself blindly to Headmaster's plans; and Harry who thinks by himself and is willing to change.
Smut and plot, nicely balanced. Character growth do not harm in any way, as well. :)