I don't know what it is about these CDs but they stick in my head and help me learn a language without even thinking about it. I've tried many many ways to learn languages and had given up, thinking my brain just couldn't do it. But Thomas' approach is easy, builds on the familiar, and gives grounding in the language so you can say useful and quite complex phrases easily within a few sessions.
I've just started the french series, but it looks every bit as wonderful as the Spanish set I listened to a year ago - and STILL remember, despite virtually no practice and cognitive problems associated with MS.
He's astounding. Highly recommended. It may not be everything to everyone, but it sure is an easy way to get started with and confident with a language.