I think one of the big complaints with Dragonborn is how much they cheapen dragons.
Dragons used to be these awe inspiring creatures of myth and power. In western mythology, they're creatures of evil, fire, poison, and pure brute strength, terrorizing entire kingdoms and destroy armies, often requiring a champion chosen by God, armed with holy relics, to defeat. In eastern mythology, dragons ARE the gods, identified with power beyond the conception of mortals. Traditionally in Dungeons and Dragons, dragons held the sort of "last boss" position, the thing you didn't even THINK about messing around with until you were very, very, very powerful.
In 4e, dragons are killable in your first few levels, and hey, look, there's one in your group!