Great fun to play with friends!
The aim is to destroy your opponents crystal/s. To do this you have a team with different powers and 5 moves per turn. If you tap on the ? mark and then on the item/character you can see all the details about each. There is a written tutorial and a video one.
I like the fact I can type in the friend's username to challenge them or invite friends to play via Facebook. You can play against random opponents too just in case your friends are taking too long in responding to your last move!
If you like to customise you can buy your avatars, heroic teams and uniform. You can also buy taunts so your team can playfully mock your opponent.
I have only been playing a few hours in between playing another game, bubble melody. It's really addictive especially as I like competitive games!