I think to me there are a couple of things that make a good website.
One is community - one site that I spend almost as much time on as I do here is a message board for a twelve step group I belong to. Badly designed, ugly colours, but a wonderful group of people.
Another is that it have something I want, for want of a better term. I go to ebay to buy or sell things, I go to washingtonpost.com to read the funnies and Miss Manners, etc. If I have a choice of two or three places that offer the same service, then, sure, I'll go to the easier-to-use, more attractive one, but I'm there for the service, not the page.