You can't really use something until you learn how, right?
So user satisfaction with a website in most cases is going to depend on how fast your visitor can learn to use the site and its fetures to get her what she wants. It is the place usability1 begins and it begins most happily when your visitor didn't give it a thought. Read Steve Krug's very powerful but simple book, Don't Make Me Think.
What's the secret? Be conventional. Wacky oddly placed menus, navigation that depends on tricked out flash movies, hidden or oddly placed search boxes, even too small type are all going to make it harder for your visitor to use your website. She won't like you for it.
Will following a conventional formula deprive my designer of creativity? Get serious. If your designer is truly creative, she will design for a conventional layout and apply her creativity to that convention. She will not do you any favors laying out a page that your visitor has to waste time, effort and positive emotions figuring out how to use.
Want examples? Practically every movie, every song, every novel, every symphony you've ever experienced was created according to a formula.
Don't confuse graphics and visual layout with web design. Like an architect, your designer's job has barely begun when she presents you with an acceptable look. The architect has to create doors where people expect them to be and that open and close, windows that do what people expect of them, toilets that do what people expect of them and so on. How much time do the occupants of the building dwell on how cool it looks?
It's the same with a website. It needs navigation that is easy to find, takes people where they'd expect to go, has conveniences like easy-to-see Search boxes. Like people in buildings, most website visitors take a quick look around and get on with what they need to do. They don't dwell on what the site looks like.
Spending too many resources on looks can kill