Vantaggi
You will get the opportunity to work with lots of other bright people on massive scaling problems. Amazon is an excellent place to work right out of college. Your mileage will vary depending on the particular group you work in but there are lots of opportunities to move between teams once on board. I have been able to secure interviews with ease since leaving Amazon and managed to sharpen my C++ and SQL skills pretty dramatically while at the company. I was given a raise every review cycle during my stay at Amazon and was happy with the salary and benefits I received.
Svantaggi
The work-life balance is relatively poor--most engineers will have to carry a pager on a regular basis. Sixty hour weeks were not uncommon in my organization. I've heard Amazon referred to as a "burn and churn" unit and I tend to agree with that. If considering various opportunities within Amazon and work-life balance is a big issue I'd steer clear from the retail and payments groups. If you enjoy building software from the bottom-up you probably won't get to do a lot of this immediately. There is a lot of legacy cruft to deal with and a lot of operational overhead is incurred as a result. I would not suggest Amazon to an engineer who is passionate about working with bleeding-edge technologies as I spent most of my time building code around application frameworks that were 5-10 years old.