Despite vast amounts of work, some web sites are not worth visiting. Take a fresh look, or better yet, show your pages to someone who doesn't fear telling you the truth. For a lighthearted approach, read Web Pages that Suck . Crashing somebody's computer with your cutesy Java applet is considered bad. Also high on the list of no-no's is anything that consumes too much bandwidth.
Graphics can be lean, fast, and beautiful, but it takes hard work.
Web site developers like to use the fanciest computers on the highest speed modems, even network connections. That's a loaded question, and the true answer depends on the audience. We could design web pages that look somewhat good on 16-color monitors. It is possible. There are JavaScript image replacement options to solve some of the problems of color compatibility, but they are rarely used.