Pros
Fantastic people, engaged, committed and clearly focused on their job. New hires will receive a heartwarming welcome and a best in class training. As an employee you will be asked constantly about your thoughts and the company certainly cares for your feedback. Bear in mind: Your work will really matter for peoples' wellbeing. Whatever will be your function, you always will feel and know: "I do something which will help to make peoples' life better." Many bright manager will try their very best to develop you and to have you having a great time...
Cons
...until the year end comes and your boss needs to have your performance made fitting to a standard distribution, following the rules of 80ths management theory (google "forced distribution" and "Jack Welch" to learn more about it) and someone needs to be at the top and someone needs to be on the bottom of the list.... As any other bigger organization, be ready to have sometimes a kind of facepalm-moment when department logic defeats common sense. My advice: This is how big companies work and it will be fine by the end. You might get higher offers in the industry, but hardly a better one. If Quintiles makes you an offer: accept it, it won't be a mistake but it will be a lost opportunity to learn if you reject it.