I don't think he's what I'd call a great player, personally. I think he once had the potential to be that player, but I think he has found himself a very good level, better than most - but I don't see a 'footballing genius' when I watch him, in the way that I did when he was younger.
Putting aside stats for a second, and just focussing on ability - I don't think he has the grace on the ball that I would associate with great #10s. His close control isn't good enough, his agility and ability to drift out of tight situations isn't there, nor a general ability to beat men.
I think he is a bit wierd in the sense that I think his skill-set is either suited to playing as a 'number 8' in a proper midfield role, or as a 9 in a proper striker role. The irony is that the #10 is often referred to as the 'Rooney-role' by many of our fans, but I feel this is the one role out of the 8,9 and 10 that requires the most grace and individual ability to play and consistently change the game. When afforded lots of space, he can be devastating. Spreading the ball left, right and centre - Rooney can do it as well as any. However, that touch of Ryan Giggs in the final third to produce magic, or where the touch needs to be just right - I don't think he has that raw genius.
Overall, I think when coupled with his longevity, he has provided an average of 8 out of 10 performances over several years - he will certainly go down as a United great.