I have owned every previous ISS/PES game in existence. Unfortunately, this is the worst.
------------------------- GENERAL ISSUES
-------------------------
Players often get red cards for tackles when they weren't that bad, and they weren't even the last man.
Players take too long to recover when stumbling through an opponent.
^ Also take too long to recover after making a successful sliding tackle, sometimes leading to CPU getting the ball before you.
Defence refuses to stay in a line. 1 player will run back 10m to play someone onside.
Players don't continue L1 one-two runs when they run into a player.
Horrible ball collision detection leading to throw-ins for the COM when it hit off the COM.
Ref's give soft free-kicks.
Fixed Player - AI ignores throw-ins.
COM can tackle the ball when they're behind you and not concede free-kicks at all. They even teleport through your player to make contact with the ball.
Players taking corners take too long to run back onside.
Ball physics are pitiful compared to PES6. The ball often bounces huge distances off of players.
------------------------- FREE KICKS
-------------------------
Ref takes AGES (ok, only a 3/4 seconds) to blow the whistle to take some free-kicks.
Turning can be slowwwww.
Passing midfield free-kicks is still useless as they usually goes to opponent as your players rarely get in a position to play a pass to them.
Passing power bar during free-kicks still does nothing.
If COM is taking the free-kick they RARELY miss.
------------------------- KEEPERS
-------------------------
Palm the ball too often on shots hit straight at them.
Too easy to score at their near-post.
Sometimes don't throw/kick the ball from hands in the direction you press.
------------------------- PASSING
-------------------------
You can use Long Pass + R2 to routinely score from the half-way line:
http://youtube.com/watch?v=5SqfV8iTtwc
If you play a through ball it just keeps going and going... it barely slows down.
Players still run side-on to the ball when recieving through balls, which often means they'll watch the ball roll out of play. Coupled with the ball momentum above this can be more frustrating than in previous PES's.
Long passes that spread play from side to side are far too fast when hit at a decent power. They're so fast that even the most talented players find them hard to control well. See this video:
http://youtube.com/watch?v=IINTj6kBh9w
Your strikers are also horrific at staying onside in general.
------------------------- SHOOTING
-------------------------
Strikers miss easy sitters. Especially when in the box diagonally facing goal.
Similarly to above, when aiming for far-post, shots go wide too often.
Shots weak at times even when power bar is high.
When receving ball quickly from rebound or low cross, pressing shoot often won't do anything and your player might try to control it before eventually shooting.
------------------------- ANIMATIONS / GRAPHICS
-------------------------
Shooting animations etc are technically good, but there's a lot of clippng through the ground, ball, and other players. There's also a lot of ice skating going on when switching animations. Far more so than in PES6
http://youtube.com/watch?v=ibsu-dm3_jM
Running animations are quite cartoony and funny sometimes, as if they've motion captured the elephant man or something.
Shirts etc have a huge gap between the skin of about 3+ inches.
Animation system makes players limbs move to IMPOSSIBLE angles to make their feet touch the ball. It usually happens with players legs and goalkeepers hands.
------------------------- CONCLUSION
-------------------------
I haven't even covered the fact that there are less options/stadiums than the previous game, and the fact that there is no Man Of The Match award etc etc etc. The list is endless.
All this is coming from someone who has thought that each PES has been an improvement on the last. Unfortunately, PES 2008 is simply not a good game. No, I don't think FIFA 08 is better, as I don't own FIFA and never will.