Pretty gentle and sensible introduction to assembly and machine code. I'm pretty familiar with 8-bit assembly already but this helped to lay some decent foundations.
The pace is a bit weird though. It starts and continues for a good deal of the book as uber simple, almost erring on the side of being patronising with it's weird 16 fingered alien - but it does just about work.
But then, as the later chapters go on, the author suddenly switches from nice and gentle to "obviously", "just" and "simple" and it feels a bit like you're tossed into the deep end with no orientation. I found I had to re-read seemingly short and "obvious" chapters.
Frustratingly the chapters on audio and graphics were exceptionally short only referring to the out ports which is technically accurate but didn't offer much advice.
Then around 40% of the book is used to build out a Frogger clone which I'll admit I skimmed.
The appendix is very useful though, with a complete index of opcode to pneumonic and visa versa which I've used a number of times already.