Hunter OTK was just before I started paying attention, but I think one of the major differences I've heard is you can play around warrior OTK to some extent, whereas with Hunter it didn't matter what you did? That seems like a huge difference to me.
It was possible to play around Hunter OTK as well but difficult. It basically boiled down to throwing down a bunch of taunters on Turn 6 (Turn 7 was the turn that Hunter OTK became possible). But this was during a time that taunters were frowned upon and the deck absolutely demolished newer players at lower ranks. This is where Blizzard started their reasoning of nerfing "unfun."
Warrior OTK is also possible to play around but it's not as easy as it sounds. Depending on your class there's a few ways to go about it but a Warrior is also going to be, actively, trying to counter your counter.
Let's look at the easiest, most consistent, Warrior OTK deck. The combo relies on the following:
1x Warsong Commander
2x Molten Giants
2x Young Brewmaster
As you can see that's 5 cards and requires 7 mana (so no earlier than turn 6 with the coin). This makes one large assumption that the Warrior is at 10 health or less so that the giants are free. At higher mana (such as 10) they can have a bit more life and still pull off some devastating results. So the idea is that the Warrior will be at a low enough health where they can drop their giants for free or close to it. Then they drop the Commander, 2 Giants and attack the face, the 2 brewmasters to return the giants to their hand and then replay the giants to the opponent's face a second time. Done right that's 38 points of damage (32 from the giants attacking twice and 6 more from the Brewmasters). It might sound difficult to get 5, specific, cards for a combo in your hand. However, the Warrior packs their deck with a LOT of card draw to cycle through their deck really fast. Novice Engineers, Loot Hoarders, Shield Slam, Shield Block, Azure Drakes, and even Bloodmage Thalnos are used for this purpose. So while a Warrior can get unlucky with draws, it's actually more consistent than you might think. By turn 7 a Warrior will have drawn a base of 10 cards if going first (not to mention what was mulliganed into) and, likely, another 10 cards or so from card draw.
The most accepted counter is to do a combination of killing them by turn 5, dropping a bunch of taunters and holding their life around 15 and then making a big push to kill the Warrior in one turn. So needless to say different classes will go about this different ways. Remember above I said that 6 cards were spent on the combo (5 are needed but a warrior will pack an extra Warsong Commander to increase reliability) and a bunch of card draw cards. The rest of their cards are control based cards. For example, you can't hold the warrior at 15 health and simply play minion after minion and taunt after taunt until you have lethal. The Warrior is going to be using weapons to intentionally bring his life off so he can throw out the combo. He's also, likely, to be playing Brawl to wipe your board of minions and taunters. If a big taunter is left, weapon to it's face + Executue.
In my opinion the deck is not fun to play against. The Warrior relies on people not knowing the combo so he can smash them early. But if you know what's coming and start to play around the combo, the game drags out for a VERY long time as you are each trying to counter the other. Some people might like this dance but it makes for exhausting gameplay.
