Design is a hard topic to tackle; on one had one could say beauty is in the eye of the beholder, but on the other had one could say functionality is king. Design is a mixture between the two, being functional and visually appealing. Form follows function is a great way to think about good design. First does it work, and if so now let's make it pretty. When it comes to websites, a good way to determine if a website is worth going back is if you can find what your looking for easily and it doesn't hurt your eyes or have tons of distractions. In most cases simple is better. If the design is just meant to be looked at and enjoyed, then we get into art which is a whole other topic. Design does matter, especially online for your websites because you want people to come to your website often and also recommend it to others. So don't go Picasso on your website.