I really liked that. A pairing which I would never have considered, but you made it work so well, and you made me care for Rabastan Lestrange, which, I assure you, I would never have expected. I particularly like your characterisation of Goyle - how he is aware of the fact that he's not smart, but nevertheless able to adapt to the situation and even take charge by mimicking Draco's behaviour. His development throughout the fic is lovely, and I would like to see what happens with this Goyle after Azkaban.
I also like how you don't whitewash any of the characters' (previous) actions. Rabastan is a torturing and murdering Death Eater, and Goyle relies on bullying and bribes, and the guard takes bribes but is still smart enough to draw the line between taking bribes and putting his job in jeopardy. All these details give the whole fic a very realistic touch. So well done indeed!