Pros
The people at McDonald's really do care about the company. They're passionate about the business and many of them have been there a long time. It's really amazing to work behind the scenes at one of the most recognized brands in the world. The culture is very caring and family-oriented. When employees are going through personal problems (health, family, etc.) co-workers really rise to the occasion and provide a ton of support. It's also a great place to be during economic uncertainty because the company is well-positioned to perform regardless of the economic climate. The medical and retirement benefits are solid and I haven't seen a better 401 (k) anywhere else. The company bonus is very generous as well.
Cons
Because people tend to stay at the company a long time, opportunities for advancement can be few and far between. When you're in the prime of your career, it's difficult to "wait your turn" for the person above you to retire. It can be a challenge getting things done because you have to get buy-in from so many people and don't want to step on anyone's toes. Turf wars can also be issue between corp and the folks in the markets who have similar roles. The vacation policy can be a little skimpy (although they make up with it if you make it 10 years because you get a paid 8-week sabbatical) and the base salaries tend to be on the lower side.