I am a bit late, but still want to talk about this card.
How can people think this card is not good enough?
Obviously, as all high-mana cost cards, it only sees play in slower metas. Many people, including myself, failed to correct judge the value of Misterious Challenger, because we thought the need to fill the deck with subpar cards (paladin secrets) would compensate for the insane "play cards for free and thin your deck" effect. It did not and misterious challenger is one of the most played cards in the current meta.
N´Zoth is basically the same concept, however, you don´t even need to fill your deck with crap to gain value. If you run Sylvanas, the card is already a 10/12 divided in two bodies with Deathrattle: Steal a minion. In Paladin you basically play with two Tyrions. In Hunter it summons two Highmanes. Dragon Priest you have Chillmaw. Rogue is the most promising though: Anub´arak, Tomb Pillager, Thalnos and the two new minions.
The biggest problem is the lack of immediate board impact. Unless you summon a Taunt Minion, the opponent may kill you the following turn before you are able to get any value from N´Zoth.