If you’re looking for more information on the transition from CreateSpace to KDP, here’s a page from Amazon that gives some great detail and further links to help. There’s been a lot of talk about formatting issues with the cover and manuscript, payment changes, cost difference, and more along those lines. Another thing to consider is language support.
If you’re having your book translated or you want to, check KDP’s list of supported languages for what formats they support.
If you already have a book published through KDP and it’s in one of the languages no longer supported, Amazon’s site says that “content uploaded in languages that Kindle doesn’t support won’t display properly on Kindle devices and will be removed from sale.”