Today Unity have released a very high quality and full featured 2D Game Kit, available here. The kit is a combination of 2D platformer game with multiple levels, a loading screen etc. It has been designed in such a way that much of the game content can be customized and configured without ever having to write a single line of code. Additionally there is a step by step tutorial series as well as comprehensive reference material that show you how to create your own 2D game using the game kit. The kit is available completely free and can be downloaded from the asset store.
If you are interested in seeing the Unity 2D game kit in action be sure to check out this quick video, which is also embedded below.