Pros
Great people, good benefits and decent work environment. I started in the UK and moved with the company to North America. The benefits are good in both locations and salaries were competitive. I learned a lot with this organization but not through traditional development channels.
Cons
Mars prides itself on "open office" work spaces and touts that this is an important part of the culture. To a degree this is true because collaboration and networking are VERY important to being effective in your work. It's a challenge for new starters to ramp up quickly because they need to be able to build their network and there is little to support them in doing so. The culture is also billed as entrepreneurial and within limits you can have a lot of autonomy. The hidden issue is that for most bigger decisions the processes are very consensus driven and this makes getting things done very slow. Over time this can be frustrating to those that want to move more quickly and lead in an agile way. The IT organization is very male dominated and they cannot seem to retain their female leadership. I often felt like I was passed over for opportunities that went to male colleagues, this seemed to be a global issue so is likely deeply ingrained in the culture, but may be limited to IT.