The problem with most folks here who 'crossover' to FIFA is that we have all been so used to playing WE/PES for years that the control/response/reaction of that game has become almost instinctively ingrained in us both mentally and physically. We are all so used to the familiar, comfortable movements of our fingers and split second decisions in our heads that go along with playing PES that of course any differing control scheme/player reaction time transition is going to be frustrating and quite possibly almost painful.
EA's approach to the game for '08 obviously is quite different than Konami in that they have tried to recreate the actual pace and rhythm of real life football and adjusting from the frenetic, barely catch your breath action of PES is going to be a shock (and quite a negative one at that) for many players. In real life it can take players a second or two to react and move (unlike Konami robots) and EA has made that part of the game.
In my view it's like this - if you want to kickback with your feet up and enjoy the easy, familiar controls and non-stop end to end action in a footy game that you've been used to for years with PES then stick with that - however if you're looking for a footy SIMULATION where the pace is much slower and can get bogged down at times (as in real life) and as you say takes hard work and battling thru frustration (as in real life) just to stay on the ball and try to carve out scoring chances then FIFA is for you.
Footy is not an easy game and neither is FIFA 08, simple as that.