Pros
I've worked here at MMC in both the consulting side (Mercer) and HR business partner side. This company consistently values collaboration, doing the right thing, and making thoughtful decisions. They reward strong performance through at-market base salaries and (primarily) annual bonus. MMC provides solid learning opportunities (formal and informal) and will promote those that contribute more than their peers in same/similar roles. It has been an honor to work at MMC and I would recommend to others - early in their career journeys or more established people looking for a company change. I was blessed with several effective leaders and mentors during my 20+ career here.
Cons
Like many large (90,000+ employee) global, matrixed companies decision making can be slower than desired. Pockets of leaders and managers that are less than effective at leading and inspiring others; however, a bright spot are executives that see this - and lead from the front.