fatal flaw
If the focus is the memory aspect (which is a perfectly good aspect to make the focus) then you need to reduce the amount we have to fight with some of the other aspects -- specifically what a nitpicky pain in the ass it is to line up just right on the arrows.
Does tapping the buttons faster make the fries and shakes faster? Because that part is kind of annoying too, especially when you're trying to rush to finish an order with more than one fry or shake.
Fix those things and I can give you an 8 to 10 score. As it is, I have to give it an "incomplete" because these things (namely lining up on the arrows) turn what should be a fun game I'd like to play into an un-fun game that I don't.