I didn't find Shuggie Bain to be depressing at all, though it certainly could have been in the hands of a lesser writer. It's not subject matter that is important but the treatment of that subject matter. A good writer connects with the reader, making him feel that 'yes, this is true to life'. He brings insight to the reader and shows how there can be redeeming touches of humanity in the darkest of settings. This is why a book like Primo Levi's If This Is A Man about his time in a Nazi concentration camp has been so widely acclaimed. It moves us with its honesty, moderation and humanity despite the horrors which it unflinchingly describes. For me a depressing book is one which is badly written and lacking in understanding of the human condition. Doesn't matter if the subject matter is all bright and breezy. It's the treatment that counts.