Ventajas
Merck has a collaborative environment with some of the smartest and most skilled people out there. The only problem is that those people all know (or think) that they are the smartest and skilled people out there, so there can be some arrogance at times. Generally though, Merck teams are great; but the hierarchy is fierce and some people take titles very seriously, and advancing is tough - but once you get there, you've made it. The work is very rewarding and of all the pharma companies out there (and I have worked for severa) Merck truly means it when they say they put patients first!
Desventajas
Old school policies around WFH for many departments. The culture is one of an old school pharma company; so as much as they try to make things hip, don't expect much of that. Oh and get ready for tons of meetings - so many that you may find it difficult to get any work done.