After Ivo Karlovic, John Isner is the best Server on the ATP tour. He makes on average two times more points with his Serve than his Rivals and when his first serve is in (which is 69% of the time) his ratio of unreturned is 56%.
Server / Very high
From the back of the court John Isner is a Puncher. He makes on average 20% more points with his forehand than his rivals but also 2 times more errors. Because of that, he does not take an edge with his forehand against his rivals on average.
Puncher / Medium
Winning only 24% of his points by the errors of his rivals, John Isner is nothing but a Retriever. Because of his heights his defensive skills are far below average.
Retriever / Very low
In order to optimize his big Serve, John Isner developped an Offensive side to his game. In total 20% of his points are won at the net (with or without a volley to play) and this result is above the general average of the ATP players. He varies well his net approaches: serve & volley, 1-2 punch & baseline approach. Howerver, his points/errors ratio with his volley is below average.
Offensive / Medium-high
John Isner is not a Tempo player at all. The quality of his backhand & return is far below average and he is not effective taking the ball on the rise.