Ventajas
It's a big company, and has the resources to offer many opportunities for training and career growth. There are also opportunities to work in different areas of the company, which allows you to get breadth of experience. If you don't like working in one area, you can fairly easily move to other areas. There are pretty clear processes and procedures for almost everything, so if you like structure, this is the place to be. Many departments, other than those with direct customer contact, have liberal dress codes. There are some nice employee-friendly perks, such as exercise centers, in-house medical clinics, etc.
Desventajas
There are many, many layers of management. This can translate to decision makers who are insulated from the information they need. Another downside is the "gain-sharing" plan which makes a nice bonus in good years but in lean years can bring your pay below what you may have planned. Because there are processes and procedures for almost everything, it may be difficult to innovate or make changes. This is particularly true with some managers who may be afraid to rock the boat. Of course, there are some managers who can apply common sense to help get the job done too.