Chrome: Wikipedia has a decidedly simple appearance. If you want to spice things up a bit, WikiWand is a Chrome extension that overhauls the entire interface.
WikiWand adds an easy to use table of contents to the side of the screen, easier to read typography and a handy preview on hover feature. For the most part, it's about an aesthetic change, but the table of contents makes it a lot easier to quickly browse an article. Of course, WikiWand isn't the only option for skinning Wikipedia, but it is one of the better looking ones.