Of all the language courses produced by Routledge, this one is probably one of the least helpful. This is all the more unfortunate as there are no other courses in Slovene available. Routledge has published some excellent Colloquial courses on Slavic languages, such as Colloquial Czech, Colloquial Russian and Colloquial Ukrainian. Unfortunately, all the Colloquial courses from the former Yugoslavia leave much to be asked for. Colloquial Slovene, Colloquial Croatian and Colloquial Serbian are all below the usual "Colloquial-standard".
For a total beginner looking for a phrasebook, this course might be of some use. It does include some basic expressions and words. However, if that is all you're looking for, you will be better served the Slovene phrasebook published by Berlitz. Not only is it much cheaper, it also includes a better pronunciation guide and far more vocabulary than this course.
If you're interested in acutally learning Slovene, this course won't be able to help you. I have listed the major problems you will face
Pronunciation
Slovene pronunciation is not easy. Stress can fall on any syllable of the word. Get it wrong, and you might say another word than the one you intended. Every phrasebook or course in Slovene I've come across shows the stressed syllable of each new word. Colloquial Slovene does no such thing, you have to guess.
Another problem is that the vowel "e" can be pronounced in different ways in Slovene. Again, phrasebooks such as the one published by Berlitz or courses published in German show the pronunciation of "e". In short, you cannot know how any word in this course is to be pronounced. The recordings will help you, but it's not always easy for beginners to pick out the right syllable to stress.
Grammar
The grammar part is what could set this course aside from a mere phrasebook. Unfortunately, the grammar part is very limited. The concept of aspect is almost totally excluded. If you speak any Slavic language, you will already know how crucial aspects are. If you're a beginner, know that you will never be able to speak a Slavic language without mastering this quite complicated feature. Ignoring the whole thing makes this course easier. It also renders it almost worthless for anyone interested in learning to speak Slovene. The conjugation of nouns is dealt with, but that's almost all there is. If you have access to Colloquial Czech (the grammar is very similar), pick it up and compare it's detailed and user-friendly approach to this course. It is astonishinh that two courses with such a variation in quality are published in the same series.
Vocaulary
Complete Colloquial Czech and you will know well over 2.000 words. Complete Colloquial Slovene, and you will not know even 900 words.
In short, this course is too little of everything. Too little help with the pronunciation, too little explanations of the grammar and way too few words.
Routledge, the publisher of this course, has also published a very extensive Slovene grammar, written by Peter Herrity. When the time comes for the next edition of Colloquial Slovene, I hope he is given the task of writing it, that he starts from scratch and takes his guidelines from Colloquial Czech rather than from this book.