Pros
Pfizer had amazing resources both in terms of financial resources and in terms of expertise within the company. Also, it was incredibly supportive of working women (or at least, my own managers certainly were), with many women (and men) being part-time or flex-time. This enabled people to have balanced family lives, and when their children needed them less, it was possible to "gear up" and take on positions of greater responsibility (one wasn't stuck on a mommy track forever). This resulted in a happy, loyal, productive workforce--at least until the site was closed. It was really great working there while it lasted.
Cons
Now that I'm in a startup, I recognize that Pfizer suffered from a very large bureaucracy that really added inertia to all kinds of things...everything from clinical trial design to contracting to...really everything. For example, now (in a startup) I can obtain contracts myself within 2 minutes; at Pfizer it took days. Sometimes a contract-in-progress at Pfizer would disappear into a black hole (such as Legal review) for weeks, and there would be nothing I could do to shake it loose. That just doesn't happen in a startup. Another thing that really decreased morale was that it was apparent that some sites at Pfizer (Pfizer had lots of sites...fewer now) were "more equal" than others, sometimes treating those at other sites like merely "hands" and not valuing their potentially intelligent input. At an extreme, this hierarchical posturing would result sometimes in an incorrect decision (e.g., a study design) being implemented because of intersite politics: if the incorrect decision came from a "more equal" site, those from that site might be less likely to listen to critiques from colleagues at the "less equal" site. In such situations, eventually the colleagues at the "less equal" site, being told enough times to shut up and just do what they're told, would give up and just become the well-paid automatons that apparently the company wanted....or leave the project.