@augustus I just re-listened to it and to me, it does not feel like it works as a three movement piece for a similar reason. Ending on a slow emotive movement like that leaves a sense of qn unresolved emotional state that asks for a conclusion, but the conclusion he chose colors the whole sonata. If you interpret it as a peice about death, than the the third movement has a sense of melancholy acceptance to it. The last movement undos this and leaves you with a sense of anxiety and dread. It feels like a death rattle to me. Like you know what's coming and you can't do anything about it and can't quite come to terms with it even though your trying. Really unusual and specific emotional color thats definitely not an obligatory bookend the way some of Beethovens early last movement feel.