A impressive website is not only nice to look at and packed with technological wizbang, but is also usable. Usable not only by the people who wrote it, but by the actual users that are going to visit the site.
This is why it's important to think about usability while designing a website, while building the functionality and while putting in the content and the final tweaks.
A good way to analyze the usability of a website is by asking yourself questions about the visitor; Why did they stumble upon the site? What are they expecting? What can they do once they get there, and how can we communicate that as fast as possible.