Heh. Late to the party as usual. I've been playing this about 2 days and it rocks.
Probably a bunch of noob observations here, but I wanted to pitch in for some reason (probably because I enjoy the game so much).
I've unlocked all the heroes and made it to rank 20 in this time, so been playing a fair amount (but still super low).
I enjoy paladin and priest the most, as I think their special abilities vibe with my preferred playstyle the best.
So I guess what I've learned so far is (I'd appreciate correction of any misconceptions I have).
1. Taunts are super, super important.
2. Having more/better minions is key. In my first few games, I would pretty much only attack the enemy hero if there wasn't a taunt around, but stopped doing that pretty soon. So maintaining control of the field is vital. As a paladin, there's nothing more fun than throwing down a consecration on a field full of totems.
3. Healing is important, but less so than I originally thought. Most of my first decks included a bunch of healing cards, but taunts, spells (like polymorph, consecration, hex, etc) are more important. Being able to avoid damage in the first place is better I think.
4. You shouldn't spend the coin on turn one, and save it for some combo or key card that's more powerful and won't get destroyed like early cards will.
5. I play paladin well for my level, but really hate going up against other paladins. I miss the cards I'm used to, and it sucks having those played against you when you know they're coming.
6. Oh, and the built in slow play cut off is awesome!
And wow, I haven't spent any real money yet, but I'm tempted to. I feel fairly adept for my status and already anticipate the staple cards of other hero's base decks. I've played arena once and went 0-3, but made a fairly bad deck I think. The arena opens up a lot more complexities and risk management that's a ton of fun. It's probably already all been said before, but I haven't read through this whole thread yet, though I will.