My 10-year-old got a Nook Tablet last year for Christmas, and has used it every single day since then. She uses it primarily for reading, too, though she does play some games as well. (She has an N2A card, so she can use it as an Android Tablet if she wants.)
My 3-year-old (almost 4) got a refurb Nook Color a couple of months ago. She does like to play games and read (or have read to her) stories, but she doesn't use it as much as the older one.
I think they're great for older kids. My older daughter doesn't have a room full of books everywhere anymore.