Terrible design: Your don't believe there's a way to use the product. You're even more convinced about that once you've thrown it through the window.
Mediocre design: You look for the way to use the product, finally find it, and think "Ah I see. I get it now...". And you realize you didn't hear what your wife just said.
Good design: You immediately see how to use the product, and think "Eheh, easy..."
Excellent design: You don't see how to use the product. You may not even see the product. You just use it, period.
