I'm just ticked that clones with a lot of differentiation, like Lucas and Wolf, were taken out in favor of new, only slightly different clones, like Lucina and The Edgy Recolor. (Dr. Mario gets a bit of leeway, because he uses Melee Mario gameplay, which falls closer to a Lucas/Ness type split.)
When customizable moves and costumes are now a thing, there's really no excuse for making a whole new character who only has the physics on their moves slightly tweaked. Especially when one of them is a literal recolor with his own theme music and a stolen final smash.
I don't hate them because they're new, or even for being the characters they are. (Dark Pit could have been an effective character if they'd been more true to how he was portrayed in Uprising, or if they had him use Brawl Pit's moveset.) I just think that Nintendo royally botched their inclusion and they should have either been skins for Marth, Pit, Mario, etc, or they should have been given unique A moves/animations and had more greatly tweaked B moves to justify their inclusion.
(I'm also irritated that they continue to the overbalance the roster toward Mario Characters and anime sword wielders, but that's a personal grievance that I can't force onto anyone else.)