Pros
I have worked here for over 3 years in the commercial organization. Regeneron has a great overall atmosphere. There are a lot of parties, educational events and employee benefits. It's obvious that senior leadership wants their employees to be happy. Because it is a smaller company you have the opportunity to take on new responsibilities you wouldn't have a chance to try at a larger company.
Cons
The review process is demoralizing, opaque, with arbitrary numbers and ratings, and goals pushing you to do more and more work outside your job scope every year (without any reward, physical or moral). There are no standards for getting promotions. If you have a difficult manager there is no remedy as HR always seems to side with management. 'Managing up' is a daily reality. The rapid growth of the last few years has brought in many individuals from Big Pharma which are quickly changing the company culture. Plenty of hiring for management and up positions. Everyone wants to be chief not indian. I.T. is the hardest department to work with; chronically understaffed, all the good people leave, and help comes at a glacial pace.