There are several non-negotiables: text must be user-adjustable, and it must be readable: ie not fashionable light grey on darker grey. There should be no more text than is absolutely necessary because people don't read web pages, they scan. There should be no waiting time for images to load because people's Web attention span gets shorter by the year: they (and you) expect the Web to be fast and efficient.
And you shouldn't have to work out how to use a site. As Steve Krug says in that wonderful web designer's bible, Don't Make Me Think , '...as far as it is humanly possible, when I look at a Web page it should be self-evident. Obvious. Self-explanatory.'