Pros
Great company goals and leadership. Excellent benefits package. Very good cafeterias. Getting to meet other people in the same field. There is a club house and gym (with excellent facilities) that's available to everybody. There appears to be opportunities for career development and support for that. Stock and 401k options. Fulfillment from doing your job since it is a biotech company that makes cancer treatments that saves lives.
Kontras
Your working experience depends on which department you work in at Genentech and may vary greatly. It's a huge company so you may get lost among the sea of people. It's a huge campus, but there are free intra-campus shuttles to help you get around. The hours can get very long sometimes, depending on the nature of your work but I'd say it's the norm for most, if not all people.