Hannibal is empathetic; he understands the pain of his victims and steals their organs pre-mortem, perhaps because he wants them to hurt or maybe he is indifferent to their pain. He is very specific about it though, it is his M.O. so I lean towards the former. But when he tries to eat Will’s brain, he has him high as a kite. There is nothing to gain from Will’s pain; he just wants Will so badly that he is going insane. He doesn’t hate him, Will is not his victim. Will is someone he must consume somehow. There is no other way.