They decided to eliminate the TTL explanation section (I think it is silly). It was already there, only a couple of pages. They corrected most of the errors based on the official errata.
The paper is a little bit thicker and flat (the 3rd edition was a little bit glossy). I haven't gone through the whole book. I'll post more if I find any other problems.
Thanks!,
I hate to be negative, but so far I don't see enough improvement to justify upgrading to the latest edition. Sure, the new chapter on programmable devices is a welcome addition. However, if nothing else got a makeover, is hard to justify buying the whole book again just for that. Let us know if you find any other improvements!