Who's it for : Anyone. Everyone. You. Unreal Engine 3 has been used by game developers, researchers, television studios, machinima directors, artists and students. If you have an idea that needs to be brought to life in a game engine, UDK is for you.
Why : Sample are provided, it's free for not commercial use. (Make your levels for free and test them).
Make concept game with your team on a very good engine. I just want to add : "You are The next-gen".