I think the data sharing is possibly a major problem-to-be in that Amazon probably getting a lot of info about me. A LOT. This is as I ramp down what I allow Google to know as I've taken steps to limit use of their products, particularly search. I think this should be people's primary concern with the rise of this service--especially as it now grows to include data on the foods you consume.
Presumably, Amazon will begin private labeling food products, which will put the company in direct line of choosing which farming practices to promote, what diets get discounted and other interesting capabilities. I want to believe this power will be used for good--such as Apple's stance toward Privacy. But benevolence can wax and wane.
I haven't heard Bezos talk about the importance of human health and the food chain, but I haven't gone looking for that yet either.
To me the delivery service via prime is still amazing. It does matter that products arrive within two days because I often put them into service the moment they are delivered.
It matters to me that the product catalog on Amazon is so expansive and has been combed over by previous buyers. The review system is not perfect, but largely I am happy with highly rated, well sold merchandise routed through Amazon's marketplace.
I also have been on the selling side of Prime and while it is expensive for sellers, it is an incredible to be able to address potential buyers using Prime with the branding and consistent experience of Amazon all over it. I'm able to sell unusual things with no reviews.
Regarding the issues you've had with that tissue delivery, I also had an issue once with a falsely advertised sizing of a ducting tube I needed for a swamp cooler a couple years back. I had to really get through to customer service to show that the product sold was not legit. They did take action on the seller after I spent the time.
That said, that was one out of many hundreds of product purchase experiences where I felt wronged and Amazon was involved.
I think we're still just getting started with the value prop of Amazon Prime.