We have had many threads like this already, here is a few:
http://www.gamesas.com/index.php?/topic/1174475-is-this-an-rpg/
http://www.gamesas.com/index.php?/topic/1177526-is-this-true/
http://www.gamesas.com/index.php?/topic/1174676-a-couple-of-questions/
http://www.gamesas.com/index.php?/topic/1174479-questions/
http://www.gamesas.com/index.php?/topic/1173479-can-someone/
tl;dr: yes it's supposed to be open-world, it's not an RPG it's an FPS, you shoot people and mutants in the wasteland, there is car combat, upgradeable weapons and cars, exploration and side-quests and bosses the size of a building. there should probably be a faq containing these stickied at the top.
Also, there is some useful info from PAX 2011 in this thread: http://www.gamesas.com/index.php?/topic/1173613-pax-east-2011/