If you enjoyed the ONI demo but have beaten your way to its end, the good people at Bungie are thinking of you.
They just released a new level for the demo. This is Level 2 from the full game and will give you a longer taste.
Just add it to the Oni folder and try it out.
If you haven't already downloaded the original Oni demo you can get that too from the downloads section.
File name: Oni_Demo.exe
File name: oni_lev2.zip