Ventajas
If you are interested in moving ahead, particularly as an Engineer, it is all in your hands. If you are smart, work hard, put in extra time, you're almost guaranteed to move ahead quickly. Politics don't come into play nearly as much as results.
Desventajas
Amazon is not the kind of place where you would pick a job and work there for 20 years. Amazon expects people to switch jobs every 2-3 years or so, work extra hours, and push hard. If you're happy with just doing your job, the 9-5 thing, it will not generally work too well. Amazon is a good place to work hard for 5-8 years, and then hop into any position you want somewhere else.. or work hard for 10-15 years and retire :) The benefits package isn't all that impressive compared to other companies, but they focus rewards on the financial side rather than benefits / time off.