Avantages
If you are on the right team, your work will have a tangible impact on millions of people, and as an engineer, it is interesting and gratifying to work on the large scale, difficult software problems. Direction is still very much set by Jeff Bezos, but to his credit he has made a lot of bold but correct decisions in the lifetime of the company. While the startup culture has faded a bit, that does mean that you can maintain a surprisingly good work-life balance while still working on interesting things.
Inconvénients
The culture at Amazon is notoriously frugal, and that can feel penny-wise, pound-foolish after a while. The startup culture that existed in the early days is also not as prevalent, which can make staying motivated somewhat challenging when surrounded by people of varying levels of motivation. In the technical career track, Amazon does a pretty poor job developing and enabling the growth of their employees, aside from the very early stages of an engineers career, unless the employee is inclined to move into a management track. This lack of career development can be compounded by the large operational responsibilities of many teams, which makes it difficult for engineers to find the time to interact with groups outside of their general are and explore other opportunities that could help foster career growth.