Here are, in my opinion, the strengths and weaknesses of the main favorite players.
Ma Long: best forehand in the world, perfect footwork, good backhand, powerful. Weaknesses: when he isn't at his best, he can get afraid of playing, taking forehands, etc. Then his opponent plays all the balls on his backhand and wins.
Xu xin: excellent forehand, best footwork in the world, excellent serve, very few errors. Weaknesses: no backhand, forehand not powerful enough sometimes
Zhang Jike: impressive backhand, good footwork, good forehand, excellent serve, mentally very strong. Weakness: doesn't take enough forehands from the backhand side, which doesn't allow him lots of variation. Forehand good but not magical like Xu's and Ma's
Wang Hao: excellent backhand, powerful forehand, good serve, experienced. Weaknesses: footwork not good enough. Not very good when his opponent has the initiative, lots of unforced errors. Simply not as good as his stronger team mates.
Timo Boll: well rounded, very good in top spin to top spin. Weaknesses: his forehand technique doesn't allow him to hit the ball fast enough, especially on drives, which makes it easy for his opponent to counter. Changes grip between forehand and backhand, which makes him lose a lot of time. Serves are too simple.
Yan an: I don't like his game and hope he doesn't represent the future of table tennis (hit all the balls as hard and as soon as you can
. Zhou is even worse in this matter ). Well rounded, very powerful, extremely (too?) agressive, excellent footwork. Weaknesses: lots of errors, unexperienced