His career here's been an interesting one. Considering the hype he came to United with, you could argue that there's an element of disappointment there in that he's probably only had two truly great seasons for the club: 2009/10 and 2011/12. That's not to say he wasn't great in other seasons, but those two are probably the only years where you could argue he was among the top 5 players (performance wise over the season) in the league, and it's also the only two years wherein he passed 20 league goals.
Despite that though, he's been remarkably consistent throughout his United career in that this is quite possibly his first bad season for the club. There have been some underwhelming ones (2010/2011 until he hit form, 2012/2013 for example), but even then he's always hit at least 10 league goals and been important. In the Ronaldo era he provided us with an excellent mix of quality and workrate: he probably suffered a tad with Ronaldo being the far better player, but was still consistently very good during Ronaldo's prime, still scored consistently, and had good seasons overall.
Someone who will go down as a club great, but perhaps fall short of ever being regarded among top 5 United player discussions.