The main difference is the be a pro mode, live season, erm, pro club championships???
to be honest, i liked 07 on the ps2
you could score from miles out lol
06 was veeeryyy sloow, and pretty rubbish, and 09 is faster than 08, and 10 is faster gameplay than 09, only on a hdtv. On standard tv i find 10 plays much like 08
In HD, it seems much more fluid. It is also easier to score from outside the box in 10, but still pretty difficult. The keepers have been improved so that it 'seems' they have a line of sight, eg they will dive late if there is players blocking their view of the ball. In 09 i found it frustrating that i could hit bullets after a corner when the box is crowded and the keeper would make a miraculous save
Pro Evo has been identical since PES2007(except new licences now and then and the legend mode-a rip off of FIFA's idea) which means it is very poor. PES6 was the pinnacle of PES life, and since it went next-gen it has been really poor