The #1 biggest problem with Hearthstone is the lack of big gamechanging cards. I started playing M:TG in third edition (we call it Revised), and back in those days there was no Type 2 and there were a ton of broken things. There are creatures that do all sorts of zany stuff like making people discard whenever they hit a player. Honestly, even that was fairly boring (and too good, according to WotC) compared to some of the stuff we saw in Legends and Antiquities sets. There was a card that made players swap life totals if it stuck around. There was a card that made both players play a sub-game of M:TG within the existing game. There were cards that let you take an extra turn! There were cards that let you pay X to do X damage. Some of these cards were super OP, others were gimmick novelties.
The trick with most of these really crazy cards is that most of them completely broke the idea of card value. A single card that cost 4 mana might be worth 2 enemy cards, or even more if it had some drawback. "Destroy all creatures in play" cost 4 mana. You could easily get 2 for 1 trades on even low-cost cards. Some cards even prevented all damage from certain kinds of sources. Imagine if you had a creature that read "Warlock spells can't deal damage." That'd be wild.
Because M:TG had such wild ideas about card value, the game design could be a bit wilder. Hearthstone is so boring by comparison, because there are fewer ways to get card advantage that don't involve dealing damage to minions by hitting them with attacks or spells. Single draws mean so much more in a game where a 2 for 1 means a huge lead.
Part of this is simply that Hearthstone strategy is so much more refined, because we came in with preconcieved ideas about card value from games like M:TG. Magic taught us about how good drawing cards is, and as a result stuff that lets us draw cards in Hearthstone is usually super valuable. Casting a spell that wipes the enemy board is usually game-ending in Hearthstone. In M:TG, a decent deck usually has multiple ways of coming back.
And really, that's my problem with Hearthstone. So much is decided in the first four turns of the game that the later game feels really meh. I hate grinding out a sure win when I have 4 creatures in play and 3 cards in hand and my opponent has 2 cards in hand. In M:TG, you could always topdeck something crazy but very few cards do that in Hearthstone. Yes, I'm aware Flamestrike exists, but that's one card, it costs 7 mana, and it's one of very few cards that actually have that kind of game impact.
I have a lot of issues with card value in general in Hearthstone, but I'll gripe about them some other time. It's still a good game but I think Blizzard's monetization is borderline scamming. Really that's worse than any card value issues with the game.