Pros
Merck is a very stable company. Only recently has Merck hit difficult times. They also remain a classy organization, maintaining the drugs on the market that save lives. Merck manufactures drugs like Gardasil and Singuair, to save lives and improve the lives of everyone on the planet . They do not spend time to maufacture non-essential drugs to treat ailments like erectile dysfunction, regardless of the fact that these pills make billions easily.
Cons
Large companies can take long durations of time to adapt and change to difficult issues. Merck represents one of those companies. The FDA also makes it hard to implement change across the organization with its large regulatory noose. This makes for a lot of documentation on your work to prove your work is helping the customer.