Mage being able to damage all minions as a base card seemed to be one of the things that made it easy to me.
Flamestrike is certainly a powerful ability, but its benefit is when you're against a lot of somewhat low health minions and you don't have enough to take them down or those minions are behind a taunt wall. However, if your enemy keeps a low minion count, but focuses on higher health minions, you'll find that Flamestrike isn't that worthwhile. Also, some classes (e.g. Shamans, Hunters, etc.) that I've seen tend to focus on higher minion counts.
Heard about the deathwing card, nasty.
10-cost 12/12 that wipes out all minions and (your?) hands! I think Ysera does something similar, but she just wipes out your hand. I've seen TotalBiscuit play Deathwing a time or two. It's one of those Hail Mary plays like a Warlock playing Jaraxus... Eredar Lord of the Burning Legion!
EDIT:
The problem I have with the wolfrider is your opponent wastes a 1/1 or some trivial card to kill it. Yes, you get 12 damage, but you don't impact the board much. With a 6/5 or something, you force your opponent to use something useful against you. You are getting 12 damage at the expense of a card that is dying next turn and whatever windfury costs you and nothing really impacting against your opponent. They still have their big cards waiting for your next play. Forcing a flamestrike, polymorph, etc hurts them and you. While you might not get that 12 damage that turn, you should still be in a decent position (unless that was all you had in your deck, and then you're likely to lose anyway).
I think the best response to this is "it's situational", which is really the response to a lot of cards. I've used a Wolfrider when I needed to take out a minion ASAP. Although, I probably would only use Windfury on it if the board was clear, because then I could focus on burning the enemy's hero. Without Charge, you'd have to hope that you can't be countered before getting to use Windfury and attack, but that's really the name of game.