Unreal Engine 3 is a complete game development framework for next-generation consoles and DirectX9-equipped PCs, providing the vast array of core technologies, content creation tools, and support infrastructure required by top game developers.
It's a great engine, the UDK is an awesome tool for beginning game developers but what I miss is Mac OS-X and Linux support.
The graphics are great, the UI is relatively easy to use and the built in scripting language is very intuitively.