Pros
Great salary, and benefits. In the US, generous opportunities for out of office needs, to make sure US employees have the opportunity to meet the amount of time European, Australian and other non-US regions have in extended vacation time. For example, 5 Volunteer Days per year to volunteer with your favorite non-profit, not just company sponsored one. This comes as an employee benefit that does not require the use of personal or vacation days.
Cons
Like most large companies, extreme internal politics. Cover up centered as opposed to actively addressing unfair hiring, termination practices by manage challenged managers. Very heavily conservative and class focused, i.e. if you are in a certain pay grade, your engagement is expected to stay within that level, and is looked upon negatively, very negatively if you try to step out of your tier, until you have been duly knighted to speak to anyone in a leadership role. Also, despite allowing employees community time, they are intentional about not being visible as Merck; they support no local causes in the communities they work and serve. Employee involvement in outside organizations is not to be shared in office, even though certain leadership members hawk Girl Scout cookies on site so that his/her team can show their appropriate support and purchase them. They are not employee communication focused; management says what you should tell, and ask about. This creates huge circles of secrecy, stunting of creativity, unwillingness of idea creation and 'facades' of innovation, at best. They are 127 years old, and really don't know or want to deviate from 'this is how we've always done it'. And that is from the top to bottom. You shall adapt to that (become Merck-ified) if you want to stay.