Depending on which game you watched, you might be very impressed or somewhat disappointed with Sean May. A lot of this had to do with him being on a relatively weak team with especially poor reserve guard play. His team was a turnover machine, and, thus, he had to carry a bigger load than just being a center. It gave him an opportunity to showcase his vast array of skills, but I think it also wore him down.
His first game was a disaster. He was completely frustrated from the very beginning by referee calls, turnovers, etc., and he picked up a technical. He drew the ire of his coach for his play and was even benched for a good amount of time. In his defense, this game didn't start until after 10:30pm so a lack of sharpness is understandable.
He looked much more focused in his second game, displaying amazing ball handling and passing skills for his size. His third game was the marquee matchup against Shelden Williams – although the two didn't play each other very much. Regardless, May really put on a show and played the entire game without rest. He was everywhere – leading fast breaks, handling the ball in half court sets, rebounding, shooting three pointers, making low post moves, and even stealing the ball from opposing guards. It was pretty amazing for a 6-8, 260lb man.
His other games paled in comparison, but that is understandable. In short, he has incredible skills for his size. It's uncanny to see such a hulking man handle the ball the way he does. He's also a superior passer, which makes him double tough to defend. Don't forget about his low post moves either. Unfortunately, he didn't get to display them much because he had to play out on the perimeter and ball handle so often.
One concern is that he didn't seem to easily establish the position he wanted on the low blocks. I believe this may be due to his relatively small legs compared to the rest of his body. This also results in him not being particularly explosive or much of a leaper. His rebounding positioning is good, but I would not say that defense and shot blocking is his strongest suit. Also, although he made some three pointers and his outside shot is certainly better than most big men, it's not his bread and butter.
Overall, he is certainly deserving of his lofty ranking and you have to really nitpick to find any flaws.