It's a great turn based game, however i can't really recommend it as a casual buy.
Don't be fooled, there is no single player mode in this game, except for some little challenges that you do by your own, while waiting for other's turns (that's why those are made for);
This game, as you may have figured out, works by turns: you and your random-online opponent do some unit movements or actions within a set amount of possible moves, submit your turn, and wait for the other's one, and vice versa, till someone win the game by destroying his/her opponent's crystals or units.
That's it, a simple game, that i like as it is. But, you know, playing with random online people at this kind of game can sometimes ruin your fun... Infact, you won't know WHEN your opponent is going to make their next move, while you had done yours minutes ago (as for me, i tend to play with people that make their turns in a very long period of time, it means they do they move and straight close the game), bringing to the conclusion to find another opponent, hoping that in the while your previous opponent will reply, or that you may find at least a more responsive one.
Just this kind of gameplay may ruin the fun of the game, without the freedom to play this as much as you want to, and i would like to play this game more often than "a single move for each opponent, then swap to other games because i'm done here".
I strongly suggest to grab a friend and play this togheter, since it's only mode is duel, to have also a real time gameplay.