So, first, comment on this post to let them know what you think of the new design. Maybe an overwhelming outpouring from the userbase may get them to retire it or at least change the default back. Second, go to browse preferences, where you can click on the screenshot of the old skin to select it. Once you do that, every time you're logged in from the same account, you'll get the old skin.
Now, I'm not saying the old skin is wondrous and perfect. It's a little frustrating to learn at first, because some of the more useful features of it are hidden in places you might not think to look until someone tells you. And the colors are kinda hokey. But once you know it, it's usable. Everything you might need is usually one click away, or two if you're on a friends or journal page. It's compatible with most browsers, and doesn't depend on scripts. And it's compact enough that, somehow, more stuff fits on your screen than with the new "cleaner" skin. There are things I think they could improve or fix, but the new skin highlights all that's good about the old one - by throwing it away.