It's the last Kindle made before someone got the bright idea that people would rather have a touch screen instead of buttons. Because apparently, when I'm reading a book, the thing I want to do is use my thumb to cover up the screen (you know, the thing that is displaying the text that I'm reading), and hold the device in a very specific way such that I can press the page when I need to while avoiding accidental touches before I've reached the end of the page.
Recently, they decided to re-introduce the majestic "button" feature into some of the newer Kindle models. You can get it if you opt for the premium deluxe "Kindle Oasis" which for some reason has an asymmetrical bezel and costs $250. (The Kindle 4 originally retailed for $80, which is where pricing for current Kindle models also starts.)
I love my Kindle 4. I use it every day and take it with me everywhere, and whenever I misplace it and need to buy a replacement, I find myself going to ebay to look for a used version of the old model so I can have a device with buttons.