Pros
I get to work with very bright, very customer focused people, who are also genuinely decent and caring individuals. I get to work on some amazing technology and I can see how it will change the world when it is in the hands of our customers. Senior management is smart, intense, focused, and driven by results. They are also very accessible via email, and will take the time to respond. There's a total lack of politics, game playing, and manipulation. The product cycle is short, so the work you do today will be in the hands of customers tomorrow. You can bring your dog to work. Having fun and helping to make Amazon a fun place to work is a core value and doing this right can even have an impact on your review.
Cons
Make no mistake, you will work hard at Amazon. This is not a place for slackers or for those who want to work 40 hours per week and then go home. The email load can be intense and the pace of the business means that you are expected to respond quickly. If you can't think, respond, act, and perform at web speed then you will get run over. Amazon's now legendary emphasis on frugality means that you will be working at a so-called door desk, and that you may be crammed into a small office with a couple of other people.