I quite like the function system, at least for now the extra backstory unlocked by swapping them around has me constantly reevaluating and trying out new power combinations. I am sure I will settle on a stable set at some point in the future but for now it seems to be fulfilling its purpose.
I am looking forward to getting a bit more memory so I can use more functions at the same time, it can't be too far off because I am already constantly hitting the limit without being able to fill most of my slots.
I was also pleasantly surprised that the little tests in the sandbox were faster and less painful than the equivalents were in Bastion, again at least for now. They give me a nice little buzz of satisfaction but don't feel like they are pulling me away from the main story for too long.