One thing that is often said about anime series, and a reason why they're "superior" to American cartoons, is that they tend to have actual story arcs and endings. The characters reach their goal and the story comes to a natural conclusion, rather than just keeping on forever until it gets canceled.
Granted, there are exceptions on both sides, with plenty of American cartoons offering serialized stories with clear endings, and anime shows that simply refuse to change and end, like...