I'd say attacking was more difficult than defending.
I've conceded three goals in 29 games in the Primera Liga and have only scored 44 goals. My goal stats in PES5 were very different.
I find the defending in open play quite easy, just depends on the timing of your tackle and the positioning of your defenders. Set-plays, however, is a different story.
The three goals that I conceded were all from set-plays. The ball would rebound off the keeper / defender and there would be an opposing player who was totally unmarked just waiting in the box to pick up the peices.
KONAMI still haven't done anything about the defensive wall. I have like a 6 man wall when the opposition have a free-kick about 40 yards out.
All in all, and the defensive wall aside, I think the defending is a major improvement as it makes scoring more difficult. And, when you do break through the defence to slot the ol' pig skin into the onion bag, it makes it all the more rewarding.