So, some stuff. Yes, max mana is 10. There are a couple cards I have that give you bonus mana for just the current turn, but I was not at max mana when I used them so I don't know if they allow you to go over that.
Unlocked the druid and the rogue by playing practice mode. Basically you select one of your unlocked heroes then you can challenge any other hero. Win and they are unlocked for you to play. Snazzy. I also fought the hunter but he kicked my ass pretty hard. Need to really get in there and handle all the creatures he will throw out. Which is a lot. I'll have to work out a good strategy to take him on, maybe fight him with a different hero.
I also unlocked a quest! Quests are a quick way to earn gold. Or...quicker way. Seems you earn 5 gold for 5 wins in random matchmaking...so saving 100g to get a pack will take a while. But the quests can earn you 40g or something and I guess there are daily quests so thats not so bad. The one I unlocked is to beat someone in an online match. I'm still a n00b so I don't know how that will go. It seems like there is no in-game chat, to keep people from trash talking and such. I believe you can chat with people on your friends list, though. Of course I'm the only one I know with the game so far so I can't really test it.
If you can get a key, play. It's great. And I'll play a round and quit, then 5 minutes later want to jump in and play again.
EDIT:
Had to play some more. I unlocked the Shaman and Priest. Shamans ability is cool. 2 mana and you will get a random totem. I saw a totem that gave a bonus to spell power, but most of them seem to be like "walls", no attack but some HP. Also Taunt so you have to target them.
The priest matchup was pretty tense. I decided to try make a custom deck for my mage and then I took it up against the priest. Things were pretty even for a while, then he got some good turns in and was wrecking me. Lots of taunts, healing almost every turn, and a bunch of creatures. At one point I was down to 8hp vs his 26hp. I barely scratched him and I was near dead! Figured it was a loss. But some lucky breaks and my heavy hitters and taunts started coming out and I pulled it off...won with 8HP. He wasn't able to hit me again.
I'm trying to unlock all that heroes since I think you get a booster pack to open once you do. That and it's good practice. You also level up your heroes as you play, unlocking new cards for them. So it's probably a good idea for me to do some of that before going online against people that probably have all those cards unlocked.
EDIT 2:
Well what the hell, I tried an online game. I was sorta worried because I picked my mage and went up against a hunter. Luckily I didn't let him build up any creatures, and I had enough taunts out that he didn't have his choice of my creatures to attack. I also had cards that would spawn extra creatures. Weak, sure. But they add up. Then I brought out my big bruiser, who gets +1/+1 for every creature I had in play. So I drop that sucker and hes 10/10. My opponent has no creatures in play. Next round he plays one but...no charge, no taunt. I can just ignore it and melt his face. Next card I pull is a 5/something with Charge. I had too many creatures in play, so I used my weak 1 damage fireball to kill one of my own weak creatures (who had a spell on her so she was 0/1 anyway and useless). Boom. Drop the 5 with charge. With all my creatures I took the dude down from 26HP to 0 in one turn.
Completed the quest! Got a pack to open and I think some gold? I didnt check the gold. Pack had some ok cards, nothing that stood out as amazing. But man, that was a really cool finish.
Oh, there are emotes to communicate with. Right clicking on your hero portrait and you options like Greeting, Oops, Well Played, Thanks, Taunt, etc. So no griefing but you can communicate a little about the game at hand.
Now that I think about it, replays would be a cool feature. With open hands, so you can see what your opponent had to work with while you battled.