I recently played on grass for the first time and will admit grass rewards many attributes of a good player: quick reflexes, bending the knees, power, volleying, taking the ball early off the bounce, quick movement. Compared to clay, which rewards stamina, consistency, margin for error. So I would say it takes a more talented player to play well on grass than on clay. This is assuming the player has more than just a big serve. Looking at all the attributes grass rewards, it's no wonder Federer is suited perfectly for the grass, and could be just about unbeatable. Few can match his reflexes, taking the ball early, quick movements.