I had an old one that had some hardware problems, and bookeen just replaced it by a 2013 one, so here the differences I've seen :
- The soft : no much differences, but it boot a lot faster (they got rid of the fancy startup animation. It's fun the first time, but when you have to wait for the device to start, it's actually annoying...). You have more options to sort your books though... You're not limited anymore to the folder structure, you can see them by author, ...
- The screen is slightly different. It seems better to me than before, but you can see a bit more the ghost image of what was displayed before the screen update.
- The back is not metal anymore but some rubberish (not rubbish) plastic. For me, it's a plus.
- There is no audio capabilities anymore (old one had a headspeaker jack for audiobooks, it is replaced by the charging led)
- no automatic orientation change anymore (manual is still there), which I had disabled anyway, kinda boring for this kind of device...
- The new power button is way better the old sliding one
- They got rid of their USB instability issue (at least is was there on my 1st gen odyssey)