I'll add to this.
Even I'm not against him. What gets to me is his inability to play attacking football. Even if I were to buy the excuse of an aging, complacent team, our attacking front four options are - Rooney, Van Persie, Kagawa, Mata, Januzaj, Welbeck, Hernandez and Valencia. If the team struggles to create more than 1-2 chances in a match despite such stellar attacking options, I think the issue lies with the system and the belief - both of which are the manager's scope of responsibility.
Everytime we've done well in matches against the 'bigger' teams - Arsenal, Bayern - we've played very, for the lack of a better word, Everton-ish. I have yet to see a match this season where we have played like we're the bigger team.
That's just not enough. I think he'll get better. I think we'll win alot more matches next season. Whether it'll be enough to achieve the standards that United fans are accustomed to? I don't think so. All in all, I think we need a manager with a stronger personality.