Very well written.
Before reading it I was afraid of my math incompetence, but this is one of those rare books which also gave all the required math (about sets and functions mainly).
Also, I found a very nice flow in the writer's style which is many times absent in textbooks. The prose flowed like a story from beginning to end.
The author had remarkable clarity about whatever he writes, even though his writing style is plain and simple.
Exemplary textbook.
Best book for Theory of Computation Courses.