i can't wait until july 31st when rott 2013 comes out!
is there a playable demo of this great game available somewhere?

Nope.

There will be a shareware episode, like in the old times. But I think it will only be available after launching the full game, so it will be "pointless" if you have already preordered the game. We will have to wait :(

The shareware episode of the old game had some of my favourite ROTT levels.