Season 1 was adapted from the novel, and the story line is the best.
Season 2 was.. umm.. ugly since they had cut the betrayal arc, and made the rest episodes as if it never happened.
Season 3 was.. ugliest, worst, and a mess! The Gayest! Too many fanservices. No character development (except Wolfram), they messed up with Sara's story, Yuuri is a dumb-always believe in Sara even though he knows he was wrong-,it's very different with Novel!Yuuri since he was cautious with Sara. And what I really hate is.. COFFIN SCENE!! IT SHOULD BE CONYUU MOMENT LIKE IN NOVEL!!!