Ventajas
Don't expect anyone to help you drive your career, it's all up to you. However, if you invest in yourself and work hard, you will find that Amazon is about as close to a true meritocracy as you'll find in the corporate world. Senior management is excellent. They are aware of the details of the business and actively help push the company in the right direction. I'm continually surprised by how very smart these leaders are and how fast they can understand and help solve complex problems. These are not backseat drivers. Amazon is not for everyone. You have to be the type of person that thrives in a chaotic environment. Every day is a new challenge. There's always some new focus of the week and you need to be able to balance your day-to-day work with the chaos going on around you. If this doesn't sound like fun to you, look elsewhere. People that seize control get control. Amazon is not about what level you are or how long you've been with the company or anything else. The only thing that matters at Amazon is being right. Speak up and back up your position with data and you'll get a lot of "street cred."
Desventajas
Amazon's a BIG company. There's simply no getting around that. This simply means that, unfortunately, there are more people stuck in big company mentality that you'll need to navigate around.