Vantaggi
Depending on the role, AWS has one of the best onboarding programs for entry/junior level employees. The company transitions you into your role rather than opening the fire hose on you day 1. The environment is laid back, no dress code, pet friendly, 10% off $1000 at Amazon.com, and plenty of other perks. Demographics are very young and diverse, with everyone willing to help. There is no 'job security by holding information to yourself' here.
Svantaggi
The only negative I've had is their base salary. Because of the additional benefits/incentives, the base salary often offered at AWS is lower compared to similar roles outside the company. With that said, AWS offers quarterly bonuses and RSUs that cannot be matched by similar employers.