Pros
Merck is a large pharmaceutical company with name recognition that will open up doors across the industry. Good benefits (pension, 401k, vacation, etc.) and work-life balance. There are several different jobs available to help those who want to know what they want to be when they grow up.
Kontras
Pay could be better. I have worked with troublesome Union but currently work with clueless management; I prefer the troublesome Union. Merck is aggressively pursuing diversity in their leadership; making it difficult to be promoted as a white male. I honestly think they hire people that are not qualified for management roles just to meet a diversity quota (yes, a legit official objective to meet diversity [as opposed to qualified applicants]).