Dieter Rams has some good things to say about good design. Exerpts are below but go read the whole thing here.
Good design is innovative
Good design makes a product useful
Good design is aesthetic
Good design makes a product understandable
Good design is unobtrusive
Good design is honest
Good design is long-lasting
Good design is thorough down to the last detail
Good design is environmentally-friendly
Good design is as little design as possible
A typographic, designological, visulicious extravaganza!