Gameplay may resemble Fallout or Skyrim, as they allow for both, that's why I asked about 1st or 3rd person.
As for the fullscreen, right now if the OS does not allow fullscreen to be on, the engine automatically switches to windowed, alternatively I also detect the following: if the player at first time executing the game, just forces quit, next time it will switch to windowed.
But your idea about the Alt+Enter is very good! I remember doing that since windows XP, I will provide this shortcut as an option as well.
Thanks!