It really isn't that great, keep in mind it gives your opponent one of the cards at random as well. if they get the 4 dmg/draw, well... you just gave them 2 cards and a pretty sweet removal.
You can't build decks around this card, because it's so random, and counting on the effect of one of the cards means youre going to be disappointed 66% of the time.
you're probably even going to be disappointed more than that, when your opponent cultists with the murlocs for a ridiculous amount of cards, or lays down a +spellpower minion and plays shiv-on-crack to kill your chieftan and draw an extra card (very possible since now he's likely at 6 mana).
I just plain wouldn't run this in a constructed deck, and the only other legendaries I would pick it over are al'akir, mekkatorque, cho, and millhouse.