This book cannot be recommended for self-study. Only some of the exercises are covered by the answer key. The same is true for the translation of the lesson texts - rather annoying since the "Colloquial Series"-books are designed for self-study.
It has to be noticed that there are a lot of carefully graded text passages and therefore plenty of opportunities to practice your reading abilities. However, as mentioned before, since the author did not bother to provide translations for every text passage, it is hard to check on your progress. Furthermore, the book introduces new grammatical features at an early stage without any explanation at all (e.g. past tense in dialog 2 of lesson 6 - past tense won't be dealt with until lesson 9). Given the fact that Croatian is without doubt a pretty difficult language to master, this can only add to the student's confusion.
Grammatical explanations are overall good. The vocabulary is well chosen - unfortunately not all of it is covered by the glossary at the end of the book, so you'd better be prepared to buy an additional dictionary right from the start.
The "Grammar summary" strikes the student as rather odd; not only does it not summarise all of the salient features of the language, as one might expect (e.g. past tense and future missing), it is also here that new grammatical elements like the imperfect or the pluperfect tense are presented to the student for the first time.
The two audio cassettes that accompany the book are excellent, no room for criticism there.
To sum up: This book is strong stuff. It is certainly not to be used for self-study, at least not for those without any prior knowledge of the language. Whoever wants to study Croatian or Serbian on their own should rather start out with David A. Norris' outstanding book "Teach Yourself Serbo-Croat".