Pros
Genentech has a great location on the Bay, so you have a great view from your office. It's a great employer if you have a family, providing nice benefits including support for commuting, day care, etc. They're #2 (behind Google) on nicest places to work for a reason. There are lots of morale events for employees, and the management is pretty open. And then there's the satisfaction of helping developing life-saving drugs, and the feeling on having an impact on people's lives. As a company, Genentech has science at it's core, and is definitely driven by the research department. The company does good science, so if you work in research, it can be very rewarding.
Cons
Genentech's campus is far away from everything, so commuting can be a problem. There is somewhat of an academic, laid-back culture, so it's slow-moving compared to the rest of corporate America. If you're not in Research or Business Development, you might be a little frustrated. Those are the two groups that drive the company. Yes, there's a lot of spending on sales, marketing, and manufacturing, but that's mostly going through the motions. If you really want to have an impact at Genentech, you should be in Research or BD.