Avantages
Amazon is packed full of opportunities. There's plenty of space to grow both personally and technically and challenges abound. The real beauty of the place is that individual groups and teams are given nearly full reign in how they operate as long as they produce the desired results. This level of freedom means that those teams which require strict SDLC methodologies to meet high availability requirements can apply those, while teams who do not require as strict of a methodology are also free to explore agile approaches. There are lots of available tools for working in certain ways, but teams are not required to use those tools and are welcome to use others of their own choosing. This freedom keeps the work environment fresh and interesting, even as Amazon has grown into a truly large company. The other aspect of Amazon that is truly rewarding is the "ownership" attitude that is fostered. Not code ownership, per se, but rather company ownership. Any employee is encouraged to think about how the project they are doing improves customer experience, drives down costs, and overall improves the business. Anyone can say "I don't think that this is a good customer experience," and people tend to listen.
Inconvénients
In short: Chaos. We haves it. I've personally witnessed complete priority shifts take place in 24 hours. If you are the kind of person who will be upset if the project you were working on for the past 2 weeks (or months) suddenly gets tabled in favor of some super ultra high priority mission, you won't like it here. Personally, this doesn't bother me. Both the tabled project and the new one will generally be interesting, and if the tabled project had a real business need behind it, it will come back around to completion one day down the road :).