Pros
Mars generally invest a lot of time and money into their associates through training and other programs. Their rewards program is very much a "package" deal, with numerous non-monetary benefits. Mars' unique culture means they are known for recruiting high quality associates so you know that most of the people you are working with are friendly, helpful and willing to work with you. Mars has a corporate structure that allows you to gain horizontal exposure (inter-departmental) if you desire it, although this will need to be driven by you to make it happen. Loyalty is high at Mars, a lot of associates feel like they are looked after and will stay with the business for long periods of time because of it. The company spends a lot of time on the principle of "engagement" to help drive productivity and satisfaction at work. Because of the globalization of the organization some horrendous hours are required (occasionally) but generally the business is "give-take" to most associates regarding work life balance. Numerous times I have found myself on the phone in the evenings and doing work, but I get a lot of these hours back by taking time off elsewhere at my convenience. Mars also heavily pushes the 5 principles, those who give these philosophies the time they deserve generally find their working life very satisfying.
Cons
In some respects, Mars doesn't "value" their employees from a monetary perspective. Salary levels are pretty set at what you sign up to, and are influenced heavily by market "comparisons" (they never divulge the specific detail) and are also compared to other associates at the same level in similar roles. Good luck negotiating a pay increase that is outside the normal development system because they are generally reluctant unless you are some kind of super hero. The "lets treat everyone the same" mentality can bring into play serious cases of "tall poppy" syndrome. Mars typically doesn't like to "promote" people doing great things, recognition is often private and contained - probably because people are afraid to single out high-performing individuals. It is hard to maintain motivation as a "high achiever" as the business treats you the same to everyone else who are doing a mid-range job. Networking and career advancement is a real problem in the organization and feels heavily politically driven. The business does not recruit/network well across business units (chocolate, food, drinks, wrigley, petcare etc) and pushes the individual (ie you) to take control of this with pretty much no support (a very difficult thing to do). Roles come and go but generally there isn't a lot of movement so trying to plan your next career move is extremely difficult. Mars has a very heavy "set and forget" mentality. They tend to rely on the fact that associates are engaged enough to be satisfied where they are until an opportunity arises, so they do not know how to cater for the high-performing and ambitious individual who desires to create their own opportunity. The business is also very global, which can be problematic as decision making from "up the ladder" that has no practical or specific relevance to the site must be followed - often costing time and/or $ for no particularly constructive reason. Challenging global direction is generally frowned upon, and a "follower" mentality is generally expected from the senior management.