Pros
If you are interested in massively scalable systems, Amazon is great to understand what true scaling means. If you are early in your career, Amazon can expose you to a wide range of technologies, and give you a a lot of responsibility quickly. There will also be a lot of people like you to hang out with, develop friendships with and so on. Amazon does a lot of college hiring, so there are a lot of like minded bright people in the software engineering areas. There is an employee discount, which is nice to have. Seattle is a great area. Amazon has a lot of tools support for software engineers, and puts a lot of effort into making it easy to build, deploy and update software.
Cons
A weird mix of micro management and a demand for ownership. One of the key concepts at Amazon is that individual teams own their product/project, and the teams are encouraged to understand and drive the direction of the projects. At the same time, there are a lot of mandatory corporate initiatives that you have to do, sometimes leaving you with very little time to do the "customer-centric" things that are supposed to be the mainstay of the engineering work. There's also a lot of nit-picking and second guessing if you actually take that ownership. Almost all engineers are responsible for supporting their own software, which is supposed to encourage the building of quality software. In practice, this means that software engineers are on-call for a week, and have to get up in the night to answer any issues that come up. Not so bad if you are on a 8 person team, which means you have to do this once every two months, but really bad if you are on a 3 person team. This burns people out pretty badly, and leads to bad code - you can't focus if you were up all night. An arrogant believe that Amazon engineers are better than almost anywhere else. I've worked at a lot of good companies, and while the new college hires are natively bright and talented, many of them are inexperienced. Amazon doesn't seem to have a lot of engineers with 10-12 years of experience, who could grow the skills of these talented newbies. I've been in places with much better engineers. But I've heard Amazon middle management claim that they can pull off extremely ambitious schedules because they have Amazon engineers. Pressure.... pressure .... pressure. A lot of demands, a lot of context switching, and a lot of statements that imply that you need to step it up and deliver.