Hopefully, I can get all of this out correctly. If not I'm sure someone will chime in and help sort us out. At the end of every PoE, there are 3 chests. 2 small chests and 1 big chest. You can level up your reputation and play as much PoE as you want but you can only unlock the big chest once a week. However, if you have a treasure key, you can play it again and unlock the big chest again. You can ALWAYS unlock the smaller chests through. So say you have no treasure chest keys and you got your big chest for the week you are playing for the two little chests and Rep.
Unless I misunderstood Ryan talking earlier, he said that the level 28 PoE big chest always gives you an exotic and I believe a Queens weapon.