Haystack my first instinct is some kind of minigame collection like warioware. another game that would fit the bill is frog fractions. in terms of board games, fluxx is like that, although I hate that one because it pretends to be simple and in reality just offloads the complexity onto the cards themselves. changing rules isn't fun when every new rule takes five minutes to read through and figure out.
I don't know how you'd make it more calvinball-y than genre changing or minigames without things getting really frustrating and unfun though. in fact I once made a game where the controls changed every time you made progress (among other intentionally sadistic decisions) and people hated it, though to my surprise they'd always play it for about ten minutes past what I expected!