When analyzing the quality of any website there are six important areas to consider.
1. Content: Content is the information provided on the site. It is not just text, but music, sound, animation, or video -- anything that communicates a sites body of knowledge. Good content should be engaging, relevant, and appropriate for the audience. You can tell it's been developed for the Web because it's clear and concise and it works in the medium. Good content takes a stand. It has a voice, a point of view. It may be informative, useful, or funny but it always leaves you wanting more.
2. Structure & Navigation: Structure and navigation refers to the framework of a site, the organization of content, the prioritization of information, and the method in which you move through the site. Sites with good structure and navigation are consistent, intuitive and transparent. They allow you to form a mental model of the information provided, where to find things, and what to expect when you click. Good navigation gets you where you want to go quickly and offers easy access to the breadth and depth of the site's content.
3. Visual Design: Visual design is the appearance of the site. It's more than just a pretty homepage and it doesn't have to be cutting edge or trendy. Good visual design is high quality, appropriate, and relevant for the audience and the message it is supporting. It communicates a visual experience and may even take your breath away.
4. Functionality: Functionality is the use of technology on the site. Good functionality means the site works well. It loads quickly, has live links, and any new technology used is functional and relevant for the intended audience. The site should work cross-platform and be browser independent. Highly functional sites anticipate the diversity of user requirements from file size, to file format and download speed. The most functional sites also take into consideration those with special access needs. Good functionality makes the experience center stage and the technology invisible.
5. Interactivity:Interactivity is the way that a site allows you to do something. Good interactivity is more than a rollover or choosing what to click on next; it allows you, as a user, to give and receive. It insists that you participate, not spectate.
It's input/output, as in searches, chat rooms, e-commerce and gaming or notification agents, peer-to-peer applications and real-time feedback. It's make your own, distribute your own, or speak your mind so others can see, hear or respond. Interactive elements are what separates the Web from other media. Their inclusion should make it clear that you aren't reading a magazine or watching TV anymore.
6. Overall Experience: Demonstrating that sites are frequently more -- or less than the sum of their parts, the overall experience encompasses content, structure and navigation, visual design, functionality, and interactivity, but it also includes the intangibles that make one stay or leave. One has probably had a good overall experience if (s)he comes back regularly, places a bookmark, signs up for a newsletter, participates, emails the site to a friend, or stays for a while, intrigued.
Info from www.webbyawards.com