I only have the demo. But I found out that PES5 is actually very attack oriented, like previous versions. At first it seemed defensive - which would have been neat.
I played on 5 star, AC Milan vs AC Milan, both on average form.
Usually I either win 1-0, draw 0-0 or 1-1, or maybe lose 1-0.
I decided to try a different formation. A very attacking 3-4-3. One DM, one CM, two AMs, and three forwards.
------Nesta--Stam--Maldini----
-------------Gattuso-------
-------------Seedorf-------
---------Pirlo-----Kaka---------
-Giraldinho---Inzaghi---Sheva---
Result? in a 15 minute half, I had 15 shots, and won 4-0.
EDIT: I just tried a 3-3-4 with Real Madrid on the PES5 demo. 5 stars, both sides average form. I scored 6 goals in 15 minutes! Had 29 shots in 15 minutes.
I did give up 2 goals, but both were from silly mistakes that I wouldn't have made if I tried to be more focused on defense
That R2 after square to shoot is very useful. Zidane scored two outside the box with that side foot.