The Question and Answer section for The Book Thief is a great resource to ask questions, find answers, and discuss the novel.
Death notices things and evaluates situations. Death is curious about humanity. Our evil and our goodness seems not so much ironic but a paradox to him. (I'm not sure it's a him, just guessing). Some other ironies are that he isn't this...
Sorry I don't know what work by John Donne you are referring to.
Death looks at the situation with childlike fasciation but does his job in a gentle way. After suffering the horrors of war, Death comes as a calming relief: Death takes away the pain.