This was just an okay textbook. There are sections of this book that are very well written (when you get into the actual start of the Combinatorics section, the author does a fantastic job of introducing the subject, provides a LOT of examples, and really does a great job of explaining what is a tough subject to many people.
But there are sections that are just terribly done. The section on non-homogeous recurrence relations was very vague, and the examples were a bit poor. The early sections covering edge and vertex covers also weren't very well explained (especially given that easier solutions using logic formulas exist).
So, overall, not a terrible book, but it could definitely use some improvement.