I love everything about this game. The circular theme is great and exceptionally well executed. Each level seems different from the other while maintaining certain aspects for continuity. Very minimalistic; everything has purpose here, and simple geometric shapes create the levels. The way that levels expand is genius, flowing very well. I feel relaxed playing this, maybe because of the excellent music and simplicity of design. Sometimes I feel trapped or restricted, but there is always a way out as far as I can tell. This adds to the calming effect even further. From the menus to the credits, this game exhibits perfect design. I am very impressed with the many new concepts used in the puzzles as well. It is truly incredible how this game is played with two controls only. (excluding menus of course) Starting out easy, circloO becomes more difficult smoothly and never gets undoable, and by the end requires a healthy amount of persistence to overcome. For what it is, circloO may be as close to perfect as anything can be. I will defer to Antoine de Saint Exupéry for a definition of perfection:
"Il semble que la perfection soit atteinte non quand il n'y a plus rien à ajouter, mais quand il n'y a plus rien à retrancher."
Translated by Lewis Galantière, that means:
"... perfection is finally attained not when there is no longer anything to add, but when there is no longer anything to take away ..."
In my opinion, there is not anything about circloO that should be taken away. circloO is a perfect game.