Actually, I read both the first and second editions this year. Was looking forward to the second edition, and preordered.
Sadly, it didn't quite live up to the impact of first book. Whilst it's mainly the same, there are a couple of areas where the pacing is a bit uneven. He has an overlong chapter on creating a clock. And his later chapters on programming in higher languages, with examples in javascript, are not as compelling as the earlier stuff.
That was my observation as well (didn't read the 1st ed.). The middle third of the book is very dense and a lot of concepts will have to be kept in mind as the CPU is built up from plain transistors. It was all new to me, so challenging.
In the last third however, higher level concepts, languages etc. are introduced, and there's nothing new or even very interesting in that part for anyone with a year or more of regular coding experience.
Sadly, it didn't quite live up to the impact of first book. Whilst it's mainly the same, there are a couple of areas where the pacing is a bit uneven. He has an overlong chapter on creating a clock. And his later chapters on programming in higher languages, with examples in javascript, are not as compelling as the earlier stuff.