I came to this game owning PES08 on the Wii and having bought (and returned) FIFA10. I wrote a review on FIFA10, so you can go see what I thought of that if you want to compare.
The main standout for PES on the Wii has always been its gameplay. Yes it lacks in graphic detail compared to the Xbox and PS3, but what is and has been truly unique is the way in which you play the game. By using the Wiimote and nunchuck you can control and move multiple players at one time creating more complex moves than possible on any other console. For me this is the true football sim.
The AI of the players has greatly improved, particularly that of the defenders. There has also been a great addition of a fatigue system, so players get tireder the longer the hold on to the ball, which works independently of their overall match stamina. This has brough a new sense of realism to the game and encourages you to play a more expansive passing style of football.
The depth of game modes has also increase greatly from PES08 (although I think many of these were brought in for PES09). The inclusion of the Champs Lge makes a very welcome appearance both in the Master League and the Champions Road set-up.
Graphics, soundtrack and commentary have all been tweaked giving that much richer an experience.
The only problem I have found is that occasionally, I am noticing some 'wobble' or 'blur' in the lower half of the screen as if the system can't keep up with refreshing the screen quick enough. I'm using a component cable and all my settings seem fine and I've never experienced anything like this in any other game.
All in all though, this really is how the beautiful game should be played!