What makes a particular design successful can be hard to define. Elegance and intuition can take a variety of forms, and all kinds of different interfaces can get the job done well.  Plus, what works for one person may be totally inaccessible to another, which is why the process of iterative design and testing is so important and such a fun challenge.

On the other hand, what makes a particular design bad is usually painfully apparent. For instance:

This and an unfortunately large, often hilarious collection of other examples can be seen in this collection of user-submitted “Worst Pieces of Design Ever.”