The two nice things about the game are its coherent cute look and its caring developer. Instead of hexes or squares, all map areas are impossibly-tall circular pedestals arising out of the clouds, and loads of units run around like ants. It's cute! The developer can be found answering questions here and on Steam, seemingly dedicated to maintain his/her audience.
Now for the mediocre and bad elements. For a strategy game, there just aren't a lot of mechanics. There isn't much choice in upgrades; they will always be the same. There isn't much choice in army composition; you just want as many units as possible. For a game about moving armies around, there is very little UI support for, e.g., selecting specific units, seeing their statuses, or directing units along a route. Also, the balance doesn't seem great. Units with absolute overwhelming strength are only slightly more expensive than useless units. Most units are useless as most mechanics, such as healing, barely work in proportion to the cost. The procedural generation doesn't work well. A map may be virtually impossible or winnable in a few seconds at the same difficulty. (For example, you may spawn in a corner with few resources and a powerful rival blocking all exits.)
Circle Empires just isn't complex enough to hold my attention. I've turned it on a few times and played one of the short games, and it played almost the same way each time. There isn't a campaign, so you will have seen everything after a game or two.