Given Apple's heritage of cool design, it's no surprise that Aperture's interface is a piece of eye candy without going over the top. It's designed for efficiency, with access to almost everything you need in the default window.
Aperture's ranking system is fairly standard with its five-star setup, but it also has a hierarchical keyword system that's easy to use and makes retrieving images efficient. Multiple options are available for organizing images into various containers, such as projects and albums. The Light Table feature works well for experimenting with photo layouts, while the Web gallery publisher makes short work of creating a Web gallery.