Post acquisition by Dassault Systemes, there was a mass exodus of key talent that has left the company.
They didn't leave because of the acquisition though, they all left due to the CIO that was hired, and the cronies he put in place. Just about none of the folks that were brought in from his previous establishment at JNJ are actually qualified to do the senior leadership jobs they are placed into today. That includes the CIO himself. Many long timers and folks that helped build the company were either terminated or pushed aside into minor positions to make more room to bring in people the CIO knows from JNJ, or diversity hires to meet numbers.
The people he brings in don't interview with anyone, they just get hired and bypass the talent acquisition process.
The integrity of the CIO is also subject. At the beginning of his tenure here he announced that he was still working at JNJ and had not actually resigned or communicated this while continuing to be employed at Medidata. Therefore, he had been given access to the office and data at both companies.
Besides that, much of the technology that is developed is interesting and innovative, though doesn't entirely work well or at scale. So, a lot of the time you will spend is fighting between different teams trying to get something to work.