I played it for some time and i have to admit that pretty much was copied from other games to make a more casual approach, like said above.
The mana management system is quite annoying. The manabase and manacurve is in magic one of the most crucitial systems, dividing decks into blitz, aggro, control, midrage, combo (via fast mana mechanics) and so on... This feature just makes up with this strategies and forces you to go from a streamlined concept to a more all-roundish one... Reducing the diversity of the game by a lot.
The attack mechanism reminds me pretty much of duelmasters, mainly because of the ability taunt, although you could at least select with the blocker ability in duelmasters, how you block.
To take that opportunity reduces player-interaction, by a big amount.
And Player interaction is a main issue. From what i saw, this was the most limited in that game. You coudn't interact with your enemy in his round at all. There are traps, but these are laughable good to play around when you know which traps your opponent can play...
This creates an atmosphere where you don't actually think about your actions at all, when you know what you will play, you can just put it into the field, your enemy cannot do anything anyway... This makes it really streamlined and easy to play.
And the thing thats bugging me at most is the class system. You are particular fixed on one class and playing a brew of different tactics is out of question, e.g. a warlock is a great aggro-hero, but he just lacks the cards to play control decks... This makes the game more streamlined, more easier, because you have a role which defines the basics of your deck, but creative deck building is almost out of question.
Luckily, many random effects can be somehow controlled (like checking to play magic arrows when your enemy has only low hwalth critters and so on), but i think this has be done to remove some issues with complex trageting (like it would be "complex" to target 3 different units....) and to nerf some cards, what could have be done in other ways, like conditions (But that would have been to hard to understand, i think...)
All in all, its, like Mojko said, a fast casual approach on other card games to get a huge mass of fans, but it just lacks the deep other card games have to bound them for a longer time...
And, by the way, the arena mode is a copied version of draft-events in magic the gathering