dawnguard: nothing really to do outside the main quest. Good guild with the vampire/dawnguard faction, but not really worth $20
dragonborn: dragon riding is limited, no spears, no playable werebears, staff enchanter is poorly implemented, azhidals aritifacts are hardly unique looking, and cost 12000 gold, main quest is severly lacking in terms of everything.
hearthfire: did what it had to do, which was setting a player home and furnishing it with a family/pets. Mods easily beat it though.