-Improve the players animations, especially the running one.It would be really cool if you will realize a completely new animation system, cause this addition
would make practically a new game in terms of gameplay if the ball physics will be like in 2010 at least.Also, you have another choice: To implement
Inverse Kinematics, EA implemented them from FIFA 07 on PS3/Xbox360, for my goodness

.
Very probably new animations will mean a smoother gameplay like never before, so one more good and very important thing

.
-Improve the 360 degree dribbling
-Improve the GK & player dives & AI
-Improve the Referee AI & update the rules of offside
-Make the turns (90 degree especially) a BIT faster (not as much as 2008/2009, though), cause low-skilled players are very hard to be controlled, and in real-life this thing is not happening all the time.
-Make different paces for PES 2011, cause some people want a faster gameplay, some people want a slower one etc.
It will be a good addition if you will make 2/3 different speeds, and in Online Mode implement this function.
For e.g. when I'm searching a match put a filter with speed (Low-Normal-Fast) then I will play on what speed I like

.
-Manual passing system, more enjoyable, more harder in same time.
That's all for the moment, hope my feedback will help, and sorry for my bad english if it's the case, I'm Romanian and I have
only 15 years old, and in my country English is
NOT the primary language.