Oh yes, my favourite kind of AU. AU but still so close to canon. And yay for House!Snape! Very fitting for him and the thing I enjoyed most about this fic. Like the part when he terrorised his patients. *g* Delightful snark!
I really liked the plot as well, with bits of mystery and inclusions of characters like Lee Jordan. And the Garden. I will have to look for it when/if I visit London again. :)
Oh, I also liked your descriptions. I could picture every scene so clearly. Especially Snape in St. Mungo's. Okay, I really loved Snape in St. Mungo's. *g*