I purchased the Leap Frog Disney Pixar Cars Project Undercover Ultra eBook for my son. My son is 3 1/2 and has learning difficulties and has taken in particular to the books on the leap pad. I do like the ebooks as for younger children the games are more appropriate than the typical games on the leap pad, which in my opinion are really meant for children 5 years +. The games that appear in this book are things like moving a car back and forth on a screen to avoid other cars etc. This book is slightly more animated than the typical ebooks you can buy on the app centre. There is movement in the mouths of the caracters on the screen (not all the time but often) and cars will drive into the scene etc. The story is pretty much a short story of cars 2 and is mainly centered around Mater.
My son has recently discovered if he presses on the words on the screen with the stylus it will say just the word he points to and he's been using this to identify words, although rather than looking at the shapes of letters etc I think he is identifying words on specific pages based on where other things are on the page (ie how close it is to Mater or a building etc). Although this does slightly worry me, I do also find it encouraging as he is using it to identify words and hopefully he is soaking up the shape of the word rather than just where it is in that book. Only time will tell with that!
These cartridges you can buy on the app store, but they are large and take up quite a bit of space on the leap pad and also are more expensive! (20 quids worth of credit for this) I would say buy the cartridge when its on sale on amazon. You can buy it second hand off ebay, but you'll probably pay more than the 7.50 I paid for it when I noticed it was on sale on amazon.