I agree with another reviewer here, PES 2010 is a very frustrating experience.
The core of its problem; the controls which are unresponsive. More often than not players are slow to carry out your commands. This is most frustrating when trying to create some slick one touch passing and your players keep inexplicably taking a touch.
When not in possession the AI players seem a bit more clever than in previous PES's. However it frustrates again, when trying to select a player it rarely chooses the closest to the ball. Often a midfielder will be selected before a striker to close down a goal kick, with sometimes 3 or 4 button presses before it selects the correct player( too late by then of course). I find this even more strange as this problem has popped up in previous PES games and been fixed since, until now.
Other (minor) problems are firstly the crowd. They chant (or drone would be more accurate) the same 1 or 2 chants over and over and over throughout the whole match. Strangely the only respite you get from this constant, repetitive, droning hell is when you score a goal; then it goes completely silent! Its so bizarre and kills any sense of atmosphere.
Secondly the animation is starting to look a bit ropey, don't think its been updated for a few years.
Thirdly the goalkeeper AI seems to have regressed to moronic, they will generally not move off their line unless called out. Again strange, as they were not bad in previous titles.
Final very minor gripe, no aggregate score displayed in CL matches, grrr!
This is a very disappointing release from the PES team. There are great improvements in graphics, tactics, licensing, and playing modes. While this may look good from a marketing point of view, I, and most other PES fans have only ever bought PES for one thing; gameplay. Unfortunately this is the one thing that doesn't seem to be improving :(