When I first started to study Polish, I used the Michel Thomas Polish Foundation audio course. I liked it. Very easy to follow, and I was able to easily retain everything that was taught. Not only that, it taught me valuable tricks to be able to construct somewhat complex sentences, considering I was only using basic present, past and future tenses. It taught common verbs that I would need in everyday situations, as well as all the question words (who, what, why, where, how, etc.) and a good assortment of linking words (yet, because, also, too, etc. ) There was also a really useful trick teaching how to take advantage of many latin-based words ending in "-tion" and adverbs ending in "-ly" that immediately increased my useful vocabulary by more than 200 words, as well as taking those same words and turning them into verbs (Seriously! It's a very useful trick.)
When I finished the course, I still felt like I needed a lot more insight into the language. There was only one case covered out of a possible seven. So I got a couple of text books and muddled my way through those. Eventually, cases sunk in. But it was a long, tough road to travel to get there. Textbooks are an absolutely horrible was to learn cases. Every single one that I've seen gets too bogged down in academic language.
The Michel Thomas Advanced Polish course was not yet available. It's now available (I think it's been out for around 6 months or so by now). I bought the course. I sure wish I had this course when I was struggling with cases. It deals with all of them in noun, adjective and adverb forms. And it does so effortlessly.
Because there was such a gap between my use of the Foundation course and the Advanced course, I had by this time already learned most of what was covered through other materials. There was still probably around 20% that was new to me, though (in fact, I did all four CDs in one sitting.) In any case, it was a good addition to my learning materials and is an excellent reference.
So in short, for anyone considering learning Polish; do yourself a favor and get both the Foundation and Advanced courses. You'll save yourself a lot of headache.