The resolution is the same between older Odyssey and Odyssey 2013 Edition.
(The higher resolution is on the HD frontlight)
The sliding on button was change with a simple push button (maybe already change on last revision not sure)
It's seems the soft was changed and some feature (PDF reflow for exemple) add into, but I don't have the old so...
Soft version 5.0 on 2013, 4.x on older, but a 5.1 for Odyssey, Odyssey 2013 and Odyssey HD was on-line for some day before being removed (some problem with the update procedure on some device (http://www.mobileread.com/forums/sho...d.php?t=200158
) so it's seem this new soft feature will be backport to older device)
An also: they remove the headphone plug