Pros
Regeneron has a bright future. The science is solid and is at the forefront of what they do. This has already translated into revenue and will continue to do so, but the most important part of this for current and future employees is that you feel like you're making a difference working here. Whether we're talking about the scientists (the real heroes), or the staff supporting them, the people working here are interested in making a difference. That translates into an overall positive working culture, and a successful company. I'll also add that the company puts their money where their mouth is. I have never been denied for materials, classes, or any opportunity to improve myself as it relates to the company's goals. Everyone is valued here.
Cons
I work in the IT department, and unfortunately, recent changes in upper management here have turned this portion of the company toxic. People are regularly berated and cursed at in front of their peers, and their efforts are denigrated. It has gone from being a place where you could make a difference and better yourself to a place where you're just trying not to be noticed.