I've been using Kindles since ebooks were barely a thing, and while the hardware has come a very long way, the user interface has been lingering. At long last, the much-neglected homescreen is being fixed. The biggest improvement is a new homescreen, which highlights your most recent books and recommends new things you should buy from Amazon. Best of all, there's a quick-access button to change light settings, and turn aeroplane mode on. Overall, it sticks with the uncluttered, flat design that Amazon's gone with from the start, but with a sleeker UI that requires fewer button presses -- especially useful given how much most Kindles lag.
The update will be rolling out to Kindle Paperwhite (2013 and 2015), Kindle (2014) and Kindle Voyage (2014) in the coming days as an over-the-air software update.