If you look at the pedigree of titles from the thatgamecompany stable you might get a better grasp of what type of game Flower is. flOw and Cloud being the first two games they created, Flower seems a fitting follow on.
The mechanics of the game are based on using the Six-Axis to move a petal through the air as if you were the wind. The goal is to bring your petal into contact with flowers scattered around the level, doing so grows your petal community in size and variety of colours. As you cause a complete set of flowers to bloom area's of grass change colour while unlocking new patches of flowers.