Simply Classy, brainy and awesome
Hierarchy of army from cheap, and weak to massively strong and expensive army units will keep motivating players to play more and more rather and end up everything in few turns. The upkeep system that regulates your units will limit your advancement and will motivate you to keep active with motivation of invasion. But the most fun thing about this game is there are lots lots and lots of different units that you can control or battle with and there are NP units that will just go around messing through the map with you as well as with your enemy. It is fun to mess back with them.
thought looks tough, learning to play this game will only take few minutes and before you know, you are good enough to challenge your friends online, easy to learn and easy to play as well.