Got a beta key in my spam box this week and just started playing today.
I've never played a strategy card game before (either real cards or digital), but I'm completely addicted. It's so damn fun.
So far I've won about a third of my online games. Any good tips or guides for a complete beginner on overall meta/game theory or class guide?
Board control is very important, it is much easier to start strong and keep up your momentum, than be behind in a game and claw your ways back into it. Your starting hand is also very important, you generally want to mulligan anything that costs more than 5 mana cost since you won't be able to play it right away. Ideally you want something to play at every turn but usually people tend to not have any 1 drops (1 mana cost card).
Learn what the different cards and hero abilities are. When you're in a game and find yourself knowing if you are ahead or behind, and thinking "these are the moves my opponent can make and could get him back in the game" and act accordingly is when you know you have made a lot of progress.
Arena is fun, but it encourages a very safe playstyle. Reliable classes such as Paladin are good to play in Arena. Constructed is a different beast, mage is probably the easiest class to pick up and play in that mode.
Watch a few streamers like Trump, Kripp, ek0p and hafu on twitch.tv to learn what their thoughts are about the different cards and how they value them which is pretty helpful for arena. They also have different playstyles so it's pretty interesting to see.
Remember that health is first and foremost a resource, so do not afraid to tap into it to clear the board. Know when some of the big class specific cards can be played: Mind Control for priest is turn 8, Flamestrike for Mage is 7, Holy Nova is 5 for priest, Consecration is 4 for Paladin etc...
More importantly, experiment and have fun! No need to mull things over too much as luck is a very important part of the game, and yes sometimes your opponents will pull out some pretty bullshit plays, but so will you in time!
Just happened to me against a warrior:
-He has 4/5 decent minions , I have 1 I think
-Use Mind Vision, Get an Ysera. Play Ysera, get a big dragon.
-Warrior uses pretty much everything to kill my Ysera,
-I play the dragon, buff him a bit and take table control.
-He plays Ysera, I use Mind control. The card didn't even have time to move, he already conceded.
Damn, Priest is such a scumbag.
Huh the same exact thing happened to me a while ago, except I was able to keep the two Yseras on the board and the opponent didn't cc. Awesome feeling!