Pros
Part of something big and generally good - Amazon is truly a customer-focused company that has brought some real value to the marketplace. Ability to have large-scale impact in your work: stuff I've worked on has been deployed on hundreds of machines and handled $100 MM+ in business. Colleagues are smart, pragmatic and get things done. The colleagues here are some of the best that I've worked with in nearly 10 years in the industry.
Cons
Operational overhead - if you're lucky you will be on a newer team without much operational overhead. Most likely, you'll be spending a significant portion of your time dealing with operational issues (pages, data backfills, investigating production alarms, resolving issues with other teams, etc). Work-life balance is hard to maintain. Very little professional development - aside from the internal speaker's sessions, there are few opportunities for professional growth and development. Email - I have grown to despise Outlook more than ever before. How can people read this much email? development process - some teams do agile, some operate in a chaotic code-and-fix mode. There's little support for best practices across the company. If you are coming from outside and have done some reading/practice in software engineering processes, this place will feel like a gigantic step backwards. HR - there is essentially no human resources department in this company. For almost all questions you'll be talking to an email alias. ridiculous upper management escalations - seriously, do you need to critique form layouts when they've been designed by a UI expert? And your background is in what, again? internal build tools and frameworks - outdated, can be frustrating, little documentation