The demo is mostly a re-creation of a sequence from Eternal Darkness, which is a bit disappointing. It looks good and all (particularly the environments and the lighting) but I would've preferred to see something I haven't already seen before.
If I recall correctly, the earliest demos of Eternal Darkness featured a playable knight-templar character that wasn't in the final game. This is probably more proof of concept than anything final, but I wouldn't be surprised if some elements of this demo were to make it into the finished game.
Assuming it is finished.