Just be aware it's in pre-alpha
Epic is making the big leap by embracing live and open development with the new Unreal Tournament. We're seeing this game getting built from the ground up and as it turns out, you can be playing it right now!
This NeoGAF thread has some basic info on what you can expect and download links to get the pre-alpha. Emphasis on pre-alpha. There's still a lot of work being done, and this is more to give you an idea of what's happening. Expect major changes all through the development.
Or, if you're like me and would rather wait for the final product, there's people playing the game on Twitch.