This isn't the only cross-platform (PC, iOS, Android) asynchronous turn-based tactical game but it great one and continues to both enterain and challenge me after move than 500 hours of play (I've spent more time via Android than via Steam)
The range of arenas, factions, faction units and special powers are more than enough to provide a depth of tactical options and challenges and when this is combined with human opponents - really the only way to play in my opinion - the longevity is indefinite.
I don't pay attention to the online leaderboards or achievements at all, I just find the core game extremely enjoyable. Each turn takes about a minute, less if there is an obvious set of moves to make, more if you have many options to choose from.
Some of the frequent choices (dilemnas!) are -
> Will you focus on winning by killing all opposing units or by killing crystals . . . and will you pursue a crystal damage lead in order to compel your opponent to make an aggressive move that may over-expose them?
> Do you risk applying power-ups to an unit in the early stages of the match, when your opponent still has specials which will enable them to gain a safe-kill?
> Do you hold back on your own specials or make use of them to gain an early game advantage?
> After downing a unit when your opponent has no healers on the board (which can ressurrect) do you stomp the downed unit or take the risk that they will have a healing option in their hand?
> Do you concede balance of power on the board in order to quickly cycle through your deck in order to hopefully draw into your hand a key unit for your intended tactics?
There are many more!
This is a fantastic "easy to learn" and "difficult to master" game,