Just really wonderful in a sort of heart-wrenching, soul-destroying way. I very much loved it, and cannot wait to read more Douglas Stuart - the way he writes was just as much a draw as what he was writing, and once I got about a quarter of the way in I was completely hooked. Some of the recurring motifs, and the movement of the narrative from Agnes to Catherine to Leek to Shuggie is so well done you barely notice the changes. 
Also I do have a bit of fondness given I live in Glasgow, but I am obsessed with books that completely wrap you up in the setting and this does that brilliantly.