Probably somewhere between solid and mediocre. Maybe if the cape was unlocked in a later world, it would be a little less easily broken, since all you really need is flat ground, which about 99% of levels other than underground, castle/fortress, or auto-scrollers have. Super Mario World giving you the cape feather in world 2 is like if Antichamber gave you the red gun as the second gun in the game (after the blue one), or Super Metroid giving you Space Jump after beating Crocomire.
Without flying thru the levels (that you can actually fly thru), the levels are actually pretty fun.
--------------------Legacy custom music
How am I so creative? I think taking walks might have something to do with it.
Every single level I will ever make in SMM2 will be easier than Ultra Necrozma.