I have been purchasing a lot of items from amazon. Mobile phone, books, etc. Here are few things which I have liked most.
Fast service: it says to deliver the product in 3-4 days, but delivers in less than 2 days only. It has no. Of offices in different places which makes it's delivery process fast.
Customer services: any fault in the product gets answered and recovered soon.
App: the app is easy to use. The option of adding product in cart and the comments on product helps to select the item easily.
Overall, I have been always surprised by it's fast service and easy user interface.