I tried to see if it was just a temporary bug, but almost all the browsers I tested displayed the black navigation bar. The only browser that still displayed the menu was Chrome, but that was no longer case after clearing the cookies.
Google indirectly confirmed this change two days ago, when the screenshots from a Google blog post included the old bar.
Sometimes, when you try to simplify things, you end up making them more complicated. Navigation elements should be obvious and hiding them in a menu doesn't make them easy to find. The huge menu took more space than the navigation bar and made the homepage less attractive. Hopefully, Google will fix the navigation interface and release a better version.