Magic's card art is the best in the business. But Hearthstone has so much more going on: sound, voices, animation, and interactive game boards. Magic Online has a few sound effects. Duels of the Planeswalkers, Magic's introductory software, is closer to Hearthstone but still light years away.
The voice work and the humor are particularly strong. When I can get a laugh by impersonating the voices for people who have never played a Warcraft game in their lives, it tells me that Blizzard has something special here.
Also, animated gold cards are much more impressive than Magic's foiling (which also tends to bend the cards out of shape).
2. Scam-free economy
When I open packs of Magic cards, a necessary followup is to research the value of rare and mythic cards. That way, if I want to sell or trade them later, I won't be taken advantage of by an unscrupulous player or game store.
Hearthstone bypasses these headaches. The cards' only value is how valuable they are to you. It's an economy of one.
Don't get me wrong: I like that my Magic cards are worth something. I could liquidate my collection to recoup a significant portion of my investment someday, if I had to. But because the cards are worth real money, Wizards of the Coast can't give away free packs the way that Blizzard does. I like that I can build my Hearthstone collection without spending real cash.
3. Better online draft format
Magic Online drafts are equal parts stress and boredom. Because you're doing everything in real time alongside seven other players, everything you do has a time limit: making picks, deckbuilding, and your overall time per round. When you're not stressing, you're waiting: waiting for a player to make his or her selection, or waiting for other games to end so the next round can start.
Hearthstone's Arena has far less stress and zero boredom (unless you count the twenty seconds or so it takes to find a match). You don't have to wait for a draft to launch or for anyone else to do their thing. You can make picks in your own time and play games in your own time. You can step away and come back to it later. Losing one round doesn't eliminate you, and winning three doesn't mean you have to stop.
While you don't get to keep the cards you draft, the rewards you earn almost always balance out, if not exceed, the gold investment.
4. New strategies
Beneath the superficial elements of summoning creatures and casting spells, Hearthstone has a very different strategy than Magic. Creatures must be protected with taunt, stealth, healing, shields, or secrets. The decisions about whom to attack, with what, and in which order can be exceedingly complex. It's also highly rewarding when you make the right call.
Hearthstone has strategic elements that would be difficult or impossible in Magic. For example, some spells and creatures like Defender of Argus care about which creatures sit next to which. Others, such as Arcane Missiles or Gelbin Mekkatorque, have random elements that are much easier to manage in a digital setting.
5. Card backs
Magic's card backs are pretty terrible, and they can't ever be updated without causing major problems for players. Blizzard has already revealed a plethora of new card backs for Hearthstone that we can earn. It's a small thing, but as a longtime Magic player this makes me very happy.
I have no plans to give up on Magic. The game has been fun for 20 years and I don't see that ending anytime soon. But Hearthstone has given me a new appreciation for the possibilities of a digital card game. I still smile every time Defias Ringleader and his lackey hit the board. A quick match can brighten my day even when I lose. That's the hallmark of a game with an enduring design. Will Hearthstone also last 20 years? I honestly hope it does.