We use the Amazon apps on our Tivo and PS4 and their interfaces are HORRIBLE. I won't even watch Amazon Prime video anymore. I want to tell it "never, ever show me non-free content" but it "forgets" that constantly. There are no good discovery tools, basically just search. It's pathetic. They have a long way to go in order to be competitive. I think their chief concern is to get you to purchase something. Prime Video is an afterthought. I wouldn't even pay $3/mo for their service.
Amazon also offered free photo storage, and it's even worse. The app (at least on the Mac) appears to have been written by a high school student. It's amazingly bad, so I gave up there as well. You get what you pay for sometimes, and with Prime that's "free" shipping only.