Even after you have maxed out the Power Up's, you will be pushed around and surrounded.  Your character is just a water balloon being jumped on waiting to pop.  There is little to no feeling of progress, even with the purchase of power ups. 

Players who like a grind for grinding sake, may like this.  Otherwise I just find it frustrating, every attempt just ends in unending swarms of minions accumulating in the centre screen, add 2 or 3 bosses, with your character kiting the edges being pushed to a wall and then death.