Brothers: More types needed. Huge power gaps between characters and items, and relax the rigid quantity requirements for each type.
Levels: Add more bosses, and make the boss of each main level random. Some bosses are way too hard for certain team types otherwise. Also, the return on investment takes too long, and their spawn points are really annoying.
Development/Progression: The first level could definitely be designed to let players pick a brother before starting the game. Progression feel outside of levels is lacking—adding some extra talent progression would be great. Also, race count has barely any presence; the content here really needs to be expanded.