A door that doesn't tell you which side to push on is frustrating.
A logo with a flowery, flowing script font is usually unreadable.
A beautiful website with no obvious call to action is ineffective.
Purple text on a blue background is difficult to read.
As a designer I believe that style is important. On a list of priorities, though, function should rank higher than form. People won't click the button to buy your book if they can't find it. Customers won't pull into your parking lot and try your food if they can't read the sign. Your website will have little traffic if the content is frustrating to read.
Clarity is vastly more important than style.