As a flash fan and a loyal Zombotron fan I can say that this game is worth playing 100% , although I would recommend turning off the connection method in the app's settings ( for android ) (to disable ads) for best experience, also the game does lack replayability after 6th replay or so ( for me ) . HF playing the game.
Also I would recommend recommend to tune the gamepad because the default - well... sucks ( some may find it comfortable but there is better options in settings ) .
The graphics are cartoonish , the movement is sometimes fast and also you can snipe zombies from afar with a simple gun ( I recommend aiming into the eyes (it counts as a headshot 99% time)).
I would call this game casual but fun.