The biggest alteration to the API is the removal of customer reviews from being sent, instead a link to the review on Amazon is returned. They are saying this is because of the high load of data being transferred and the keyword of the entire update is ‘Efficiency’, while I do not doubt this for one second, I do suspect that this is a change to give their own site a higher set of results in search engines, by keeping their unique content (reviews) to themselves.
This is no real bust up for Affiliates that actually use proper, unique content. Google has always said (and pretty much kept its word), if you give people a reason to come to the site, they will. You can never go wrong with unique, quality content, its is key to a successful Affiliate (and website) campaign; As I know all to well from the blisters on my fingers from typing so much.
There are some other response groups that have been removed, never used any of them and you can see the full details at https://affiliate-program.amazon.com/gp/advertising/api/detail/main.html