Definitely check out a smaller game like Mordor first to see if that fantasy genre appeals to you. Mind you, Mordor is more of an action game with only slight RPG elements. Witcher is full on RPG which may be tantalizing to someone who hasn't played many RPGs!
Yeah man, the open world is what grabs my interest the most. The video reminds me of one of the gameplay videos Red Dead Redemption had back in the day and this seems like the next closest game to it lol. I'll play Mordor first and then I'll know if I really want this game or not!