Caramel Onion

Something which seems to be good at first, like a caramel onion at first appearing like as a caramel apple, which then turns out to be bad or disappointing when you engage with it, like when you bite into a caramel onion and find out that it is not, in fact, a caramel apple.

Diablo IV is a caramel onion.

Not sleeping for 34 hours straight is a caramel onion.