He's a very good player and his overall game isn't nearly as terrible as people here make it out to be, even though it's not great
But he does seem to struggle against higher quality of opponents/importance of the game, at least since moving to United. IIRC he didn't really have this problem at everton, remember him scoring a few against the best teams in england as well as derbies
Off the top of my head the only big games i remember him doing well are chelsea at home(united-chelsea 2-1), brazil at the world cup and of course the greatest night on the caf in the last 6 years