The most important factor that makes a great website is the user interface. If the visitor is having a hard time navigating through the website, then they will most likely close the page. Look at Amazon for example - one of the worlds most profitable companies, why? Because it puts the customer first.
“If there’s one reason we have done better than of our peers in the Internet space over the last six years, it is because we have focused like a laser on customer experience, and that really does matter, I think, in any business. It certainly matters online, where word-of-mouth is so very, very powerful.” - Jeff Bezos