I don't even really have a problem with the fact that the free to play is a bit of a carrot on a stick, but yeah, it barely qualifies as F2P. It's the kind of F2P where you're allowed to play the game for free but you're never realistically going to reach the top unless you just grind arena for two months to assemble a mech mage deck and then play that to legend and consider it having reached the top.
My concern is more with the insane investment it takes to get somewhere even when willing to pay a reasonable amount of money. After a ?100 investment (and yes I did buy Naxx), I've only just become able to put together the very cheapest of the top decks, and then only by disenchanting virtually every card I have that isn't used in the meta. Unlike games with leveling and a gearing-up process, this isn't a game where the journey is particularly great, there's no inherent value in playing shitty budget decks until you can afford the good cards. As such, requiring such a long, mindless grind to get anywhere is silly unless the alternative is reasonably priced.
Hearthstone clearly has a severe mismatch between the time it takes to learn the game and the time it takes to obtain the cards to make advanced decks -- unless one is willing to throw several hundred euros at the game, of course, but that's objectively ridiculous. If you don't do this, it takes way longer to obtain a good deck than it takes to become a good enough player to warrant playing a top deck.