Start with Roy Vagelos, and the company goes downhill from there. While a forced retirement, he was still healthy, a sginificant force in the company and the industry, and in hindsight, probably the rudder on the ship. Why was he not kept on as Chairman of the Board until the mandatory retirement age for Board members?
What is the primary reason that talented people have left Merck? Simple, the Merck of today is not the Merck that was named the most admired corporation in America for 7 years in a row in the late 80's and early 90's. It was innovative, and had a rich pipeline of commercially attractive products. People enjoyed working for Merck, and were richly rewarded for their contributions as their stock holdings and options increased in value. Salary and bonus is not enough - you can get that anywhere.
The last major product introduction was Vioxx in 1998. Since that no longer exists, go back to Singulair in 1996, or 10 years ago. No company can grow with such a lackluster performance on new product launches, especially one that has a string of current and impending patent expiries. The math is simple to all but Ray Gilmartin (the person we miss the least).
What I most miss is the "old Merck", and I don't believe that we will ever see it again.