Written as a text book for freshmen who were going into engineering and programming - at one of the top schools in the country.

I've only been close to the level but I believe freshman courses of those sorts often involve throwing really smart, cocky kids to a given subject in the most challenging fashion possible. (Remember Caltech used the Apostol text book for calculus, developing everything axiomatically, because, you're smart).

So it is introductory text but it might not a gentle, easy introductory text.