Dr Force, have you played PES recently? I have PES2008 on the PSP and the pressure is on all game from the CPU, it never stops. I've posted it a few pages ago so I won't repeat it again, but I had to stop playing it on the PSP now that I've played the FIFA demo (and I was playing it for a few months, was enjoying it too).
It's less responsive in certain situations and the CPU cheating is far worse. You notice it as soon as you kick off; if a defender is near you it takes two seconds to register your button press so that they can get the ball off you, and if you're sprinting your player will magically decide to knock the ball ahead 15ft if you're anywhere near the goalkeeper, who will then pick it up.
You probably will get fed up of it after a month - that's no disrespect, that's just how it is, especially when you're playing the AI. No AI can be completely original and surprise you 100% of the time, it's programmed, it can't develop itself to be different every game. But the AI is far superior (team-mate wise and opposition wise) than PES and with far less cheating. IMO, of course, but I've played PES2008 on the PSP solidly for a while now.