I would've liked to see Brinstar Depths from Melee back. It made for some fun games in Melee. (The first time my friend and I played it, he was camping on the island, waiting for me to come over. The stage turned and he fell off)
Honestly, the stage selection built-in doesn't matter to me as much as the lack of stage builder options. Why can't I make moving stages or rotating ones, instead of just putting random platforms down?