wrong era for him. his serve and FH are very powerful but his movement, BH and ROS is lacking.
I think on the fast 90s grass he could have won wimbledon. I think isner is one of the best servers ever, probably better than pete (2nd highest hold percentage ever despite the conditions of the courts).
of course he would still not be the favorite over pete or becker since those were much better players but I don't think his overall package is worse than krajicek or goran.