I am enjoying the hell out of this. I was a magic player from 98-00 but did not have the time to continue once my first child was born. I am still sitting on a hoard of Duel lands, beta serras and other cool stuff. (I did sell off my power 7 prior to leaving the game though).
I am largely a free to play guy, but I will pay for the single player content in order to gain access to those cards. I find if you are patient and you grind, you don't need to spend money to compete with deep pockets.
There is a crafting system where you can salvage cards you earn in packs and put the materials toward building the cards you need. So while I have not pulled any of the best legendaries, I will be able to make one very soon. I do the daily quest (which requires you to win anywhere from 2-5 games to pay off) and doing this nets you 3-5 packs a week in maybe 30 minutes a day of play time.
You can make competiive decks for hunter, paladin and druid pretty quickly that will enable you to grind wins and complete your daily quests.
Once you have that going, you can craft a few rares to make a deck that competes against the deep pockets and wins a good percentage of the games. Pick the hero who suits your playstyle but I would shy away from warrior unless you willing to spend a bit. Any other hero you can build a good deck in matter of weeks.
I have not yet made it to the top ranks. I usually finish the season ranked somewhere on tier 8-12 and have a solid win percentage against those with "all the cards". But I am not yet able to beat the very best players consistently.
If anyone wants to get into this game and wants help with deck construction, my handle is ENNUI on battlenet. There is also a nice spectator mode where you can watch your friends play and pick up strategy and decks that way.
People are pretty good about becoming friends and allowing spectators as the daily quest around 1-2 a month is to spectate another's match for a free pack.