I love the XIV's, but I don't think the XXI's are that far behind them in terms of performance. I like the higher cut on the XXI's a lot because it gives more stability around the ankles, and the traction on these are pretty great. These are definitely my favorite pair of J's since the XIV's to ball in, and the heat/ventilation problems can be solved with the right type of socks just as everyone else has said before. I'd give them a 9/10 or 9.5/10.
"My attitude is that if you push me towards something that you think is a weakness, then I will turn that perceived weakness into a strength." --- Michael Jordan