I cancelled Prime late last year, and haven't really missed it, either.
Leaving Prime also meant the end of free Amazon Prime Video (you can still rent or buy many movies without it), but I’ve been able to bear it.
While I had Prime, I think there was 1, maybe 2 instances where I wanted to watch something and it was actually included with Prime. Every other time, Amazon Video had the movie, but they wanted an additional fee to watch it, so this was absolutely no loss.
One thing to note: Every time I check out on Amazon, now, they offer me a reduced price 1-week "trial" of Prime, to get the expedited shipping, for like... $5 or so? If you cancel yours, and also see this offer: You can take the offer, submit your order (and get the free 2 day shipping), then once you get the shipping confirmation, go in and cancel the Prime subscription. Since you've had it for only a few hours, Amazon actually refunds the price you paid. In effect, you get the shipping benefits for free. We'll see if they close this loophole, but for now, it works.