I've been using a new Kindle Paperwhite recently.
I haven't used a Kindle much before, although my wife has one, so I can do some comparison. What I'm really comparing to is reading on my iPad (1) with the Kindle app.
I wasn't sure that it would be much better than reading on the iPad, which is why I've put this off for this long. Reading on the iPad is just fine.
Reading on the Kindle is better.
The resolution is now quite good, 212ppi, and the page turning action is pretty fast. I thought I might get annoyed with the page turn time, but this is just fine. Almost not noticeable - slightly faster than the previous Kindle model.
I didn't think I would really want to use the Kindle PW light. But you can't actually turn it off. But that's ok because it is actually really good, unobtrusive, and just fills in that bit of contrast when you need it, and is effectively gone when you are in good light. It's perfect in bed with the lights off, and its great in the sun, of course. There is a slight unevenness to the light at the bottom of the screen, as reported in many places, but isn't annoying.
The time left to read the chapter (and book) feature is pretty cool, so when you are thinking about putting the book down, you can see how far away the next chapter is easily.
I haven't used the X-Ray feature yet. It may be more useful after finishing a book, if you wanted to check out the characters further I suppose. And when the book supports it.