Incredibly modern read. It is clearly visible that this book inspired modern CS books on the same subject.
Personally, I found it very interesting that Wirth (who I knew as the creator of Pascal) decides here to start from types and in particular from enumerative types. It seems that to him the modeling aspects of programming were central to discussing CS topics.
I also found interesting to see that Wirth considers his readers as fluent in mathematical topics such as algebra, number theory, and in general that probably matched the situation of the 1970's were people learning about Computer Science came mostly with a strong math background.
A final node: many of the data structures and algorithms discussed in the book are central to CS today as they were at the time the book came out, but I have to say that Wirth has a terrific way to introduce and motivate the need for these structures and algorithms, and in most cases they are much clearer than in any book I used when I studied CS in the 90s :)