I'm not doubting the lad has talent but since he was at Everton and Euro 2004 he hasn't produced the same sort of displays against quality opposition. This for a number of reasons.
1) Not being played consistently( if at all) in his suited position as a 2nd striker
2) Has lost the 'unknown' tag that he had at Everton & Euro 2004 meaning teams know what his strengths are.
3) Media hype built him into a world beater and he has fallen short (not by his own fault) of these expectations
4) The succes of Ronaldo who is of similar age and was half the cost of Rooney, leads to fans seeing him as an underachiever.