mikaelis
Prophet
My impression is that they themselves don't completely know so far how it is supposed to play, with the exception that they want it to have an as realistic as possible (in the limits of gameplay) open world.
We will see if they succeed with that (I'm a bit skeptic).
I think they have general things worked out, e.g., it has first person perspective, real-time gameplay, no magic, no monsters, open world. They also have a sketch for the setting - historical, medieval central Europe, Hussites wars, taking place in the small piece of the world but without too much scalling down the distance (though this is not confirmed it will be actually in).
What is not there is details about mechanics, e.g., horse mounting and fighting, how realistic physics will be, character progression (if any), stats (if any), cRPG mechanics (if any) etc.
Also, they probably won't have story at this point (otherwise they would probably blog about it).