Hearthpwn

Yeah.  I created the first version of this deck before Kripp made his video.  I added N'Zoth after seeing his video.  The deck isn't very refined.   I only played about 10 games with it.  I'm waiting for Purify to come out so I can refine around that.  I don't expect the deck to be very good, but it will be fun to toy around with when I want a break from traditional decks.

Arcanosmith is a great substitute!  I didn't even think about using Karazhan cards.  The main reason I posted this deck now is because the Karazhan patch contains AI fixes that make most of the Heroic Skelesaurus Hex decks on HearthPwn not work anymore.  (Namely the ones that exploit AI bugs around Kel'Thuzad or Animated Armor).  

Priests are tough.   I removed Acidic Swamp Ooze and added Doomcaller to resummon C'Thun for more lategame punch against Priest.  I'm probably at about 50% winrate against Priest now.   At ranks 20 thru 15 I am seeing way more priests than weapon users, so this has been OK.  

Those are big cards to be missing, so you might not do well without them.  Instead of jaraxxus you could run a second heal card like Earthen Ring Farseer, Cult Apothecary, or Refreshment Vendor. Sylvanas Windrunner is notoriously hard to replace as it's one of the strongest cards in hearthstone when played correctly: you could try Loatheb or any other 5 / 6 drop that you like -- maybe a taunt.

I think it is a central card in this deck. It:

1. Can be a major board control shift (tempo) on turn 7, 8, 9, or 10+ when it summons an extra taunt
2. Can keep you alive while you wait to draw healing (12 hp of taunt divided over two targets so it is resistant to removal)
3. Is an absolutely amazing 10 mana combo with Brann for an extra 4/6 taunt, that often is a game-winning play.  
4. Regarding the Brann combo, often the 3x 4/6 taunts keep your Brann alive for a winning Brann + C'Thun combo on the next turn

A replacement would be some other large taunt or more AOE, but the deck will suffer seriously in my opinion.

Leeroy is useful in many decks.  Avenging Wrath not so much.

What is "play potential" and why is it more important than winning?

I built a similar Druid deck for myself (not netdecking) and it worked on the 2nd try (revised a few things).  I think it relies on luck a bit less than this deck.  But, sometimes the need for luck cannot be eliminated.  The game has random elements (chiefly, what cards you and your opponent draw is random).  If they make the boss hard enough, sometimes the randomness sets you up to fail, unavoidably.

I have basically every card in Hearthstone, and each of my 9 slots has a very strong deck.  I'm not bragging; I just have no life and I play constantly.

I can play about 2 of those decks well enough to get past rank 15 in ladder.  

The other decks I suck at, so I never use them in ladder, because I lose rank quickly with them.

The daily quests often require that I play my non-main classes.  Instead of losing ranks while doing my dailies, I choose casual.  Yes, my decks and my experience blow newbies out the water.  Sorry, I'm not going to lose ladder ranking (avoid casual) just so newbies can have a safe place to win games.  If I'm a tryhard or a jerk because of that, so be it.  Sorry.

I assume many people do the same as me.  Thus, casual is not safe for newbies and probably never will be.

MMR relies on giving the game a good sample size of your talent*deck.  That means you need to play lots of games.  That's how statistics works.