Ventajas
Marsh is a large company that belongs to the MMC umbrella of companies. There are over 60,000 colleagues in the operating companies together. This creates lots of opportunities to meet some great people that could possibly open doors in the future. Salaries are reasonable- not much different than typical market value. Their 401k program is generous, as they give you a standard 4% contribution on your base salary (without you even needing to contribute!). Job security was better in the past, however as things are changing within the organization we've seen layoffs and stream lining of operations. Other than this, it's a standard work environment. The culture is neutral, not overpowering but not lacking.
Desventajas
HR is truly a mess. I was offered an internal transfer verbally, and was subsequently dragged along for almost 6 months before I pulled the plug and found another job outside of the company. Raises are almost non-existent. Don't expect anything more than 2%, and in most cases 1% is lucky. Some departments are better than others. I won't elaborate much more on this, but be careful when accepting a position and do your research.