FallFury is an open source 2D game for Windows 8 released on CodePlex, http://fallfury.codeplex.com/ 

You play as a bear that falls down from the sky, collecting buttons, avoiding obstacles and fighting monsters. Here's how the site explains the concept,

"This project demonstrates the capabilities of Windows Store hybrid applications, leveraging both the power of DirectX and XAML. It also supports an extensible level model, where developers can adjust the character behavior and the item sets by modifying specially designed XML files."

   

This 11 parts relative to FallFury on Channel 9 is an extensive series that will guide you through mastering skills to develop Windows 8 games,

1. Introduction

2. Shaders

3. Basic Rendering and Movement

4. XAML Interop

5. Creating Levels

6. Rendering Level Elements

7. Animations

8. Element Interactions

9. Particle System

10.Charms

11.Hardware Testing & Debugging

12.Conclusions