I'm giving Amazon.com's Prime service one star for the following reasons:
1) Deliveries are a nightmare. Even with very specific instructions about where our mailbox is, they can't seem to get it right. They have been ZERO for THREE with my last 3 orders. They refund my money, but it is still discouraging because you don't get what you order.
2) Content services (like Amazon Music and Video) deserves negative stars. Nearly every single Amazon produced movie or show contains the F-word. Even a cooking show had the F-word in it several times. Music is typically covers of popular songs, and if you want originals, they want you to even pay more money. (You're already paying $120 a year!) They also have commercials! It's a paid server, and you still get commercials.
3) While the free shipping may be worth it, and I'd give it 4 stars (which have have discounted my overall rating for the reasons above), it's not worth much if you don't get your order.
I do like their return policy. And they make it easy to find what you're shopping for, they have some very serious problems which need to be address with their shipping.
As to their content services: It would be nice if they unbundled it and offered a Prime membership without digital content. That said, you're really not getting much as far as content goes. You get more free from Pandora and various channels on a Roku device.
Bottom line: If you think free shipping will pay for itself, then go for Prime. Otherwise, don't waste your money.