I love this game and do not foresee myself quitting any time soon. It's pretty balanced and fun, with room for ample creativity (to a certain extent... truly competitive decks are still a little pigeon-holed). I've played a while now and am pretty good at it - which I only mention because I don't want people to read this and think I'm just some new kid griping because he keeps losing to mages.
In constructed-deck play, mages are fine. You can get plenty of synergies going within every class that make your deck hard for mages to deal with. So when I drop my bluegill warrior on round two with a hunter, I get to watch him hesitate as he agonizes over his decision to ping it to death or get something on the board. It's a tough call, because he knows I've got a rush deck going, and if all he ever does is keep the board clean he'll lose by turn 6. I'm affecting the game, and it feels good.
The problem is in arena. While arena is a blast and I love it, the nature of the beast is you can't get synergies going nearly as well. I can't really draft a rush deck. To some degree I can try, but I'm going to get some cards that don't fit, and otherwise bypass stronger cards for weaker ones simply because they fit my theme. All in all, not a viable strategy. Not a huge deal, arena's still fun, but you have to rely much more heavily on individual card strength. Herein lies the problem with the mage; she has just too many cards that are killer on their own. Frostbolt only costs 2 and knocks out many minions that take 3 or 4 mana to drop. Fireball costs 4 and is negating minions that cost me 6 to get out. Then you add in the hero power to even further fine-tune the out-valuing domination, as it severely reduces the strength of divine shields and certain death rattles. Then there's Flamestr... ugh. I don't even want to start on that card.
Anyway, repainting the same situation in arena play, mage vs. hunter, hunter drops bluegill on round two, mage's turn... yes it depends on the hand what you do, but just pinging it to death is a pretty strong play here in arena mode. You're trading the 2 damage you already ate to be up a card and have no real fear of this deck being organized enough to kill you any time soon.
But, you guys play the game too, it's not like you need me to tell you playing mages remains frustratingly non-interactive. You've been there... pretending like your choice between dropping bolderfist or sunwalker is an important decision, deep down knowing either one is getting polymorphed.
Anyway, the humblest and subtlest of suggestions, pluck out some of these cards that stand so well on their own and simply up the rarity of them. It doesn't change anything within built-deck games (which doesn't need changing in my personal opinion), but would at least make the hopelessly OP mage deck a rare encounter as opposed to a commonplace one.
Everybody Who Has Ever Played This Game