Personally: I don't care too much about the memory size. I never even got close to using 2GB with my current one. And if they only traded the 2 gigs for the display light + better resolution, I'd be happy. Then again, how much more do 4G cost Amazon in hardware (manufacturing) costs, vs 2G? Probably a dollar, if not less.
I can't tell about the 4 bit vs. 8 bit framebuffer - I'm not sure I'd notice it while reading books.
The one thing that bugs me is that they took away the sound, thus clearly cutting away one of the previous features.
And of course, stating it again: I'm pissed because only people in the US can (pre-)order it.