Pros
Medidata has a willingness to look at what it should rip up and do differently. There does not seem to be as much red tape that you get in larger companies, although there are a lot of systems. People are kind and the vast majority genuinely care about what they do and want to make the company great. Compensation is good and benefits are excellent compared to other companies. The HR people I interacted with seemed very sensible and approachable and I had a good recruitment/onboarding experience.
Cons
Communication is bit erratic. People sometimes hear what's going on through rumour or indirect channels. It is US centric and doesn't feel like a global company even though there are offices in places outside the US. Don't always know what's going on globally. Other than that, not seen anything else I would improve!