I've gone through all 3 full sets of Pimsleur Mandarin Chinese. If you'd have asked me immediately after I'd finished them what I thought of the series, I'd have given it 5 stars without hesitation. However, after spending the past year trying to advance past what I've learned via the Pimsleur series, I've come across some reservations which prevent me from giving it a 5 star review anymore. While I do feel the Pimsleur method is incredibly useful and (despite its seeming simplicity) very innovative, I think their Mandarin Chinese series also suffers from simply being "plugged in" to the standard Pimsleur format, rather than receiving the customization that would help users truly understand the Chinese language, which has many quirks unique to it.
My reservations:
1) Pimsleur Chinese teaches the Beijing version of Mandarin, which is understandable considering it is the "official" Mandarin dialect according to the Chinese government, but the fact is that the vast majority of overseas Mandarin speakers do not speak Beijing Chinese and may give you puzzled looks when you use the phrases taught in this series. For example, in Beijing the word 'where' is said 'nar', while just about everywhere else (Taiwan, Singapore, and other parts of China) they say 'na-li'. Sure, 90% is probably the same, but that 10% that is different can be very confusing. Occasionally they give alternate ways of saying words, but more often they do not. Native Mandarin speakers may understand your Beijing usage and pronunciation, but you will definitely need to re-learn several key words in order to understand when they speak to you.
2) Classical Chinese, I believe, was basically mono-syballic, but Modern Chinese is heavily composed of compound words which can be broken down to their individual components as a mnemonic and as a way of better understanding the language. However, Pimsleur rarely does this. For example, I noticed they gave several words that began with dian (which, via other means of study, I learned means 'electronic'), such as dian nao (electronic + brain = computer) and dian hoa (electronic + speech = telephone), but I had to look elsewhere to understand the individual components. Pimsleur breaks down a compound word maybe a quarter of the time, but it should have been done EVERY time.
3) Although I still believe Pimsleur is a great introduction to the language, you ultimately only learn a VERY limited vocabulary from the entire 3 sets -- maybe a few hundred words -- not nearly enough to understand a TV show or movie (again, especially when you consider you are only learning how to say things in Beijing Mandarin).
Don't get me wrong, Pimsleur does an excellent job of getting the listener to memorize key words and phrases using good pronunciation (my Mandarin speaking friends were quite surprised by my "clear, classical accent"), but it is only a first step. To continue learning Mandarin, you definitely should learn Pinyin (i.e. the method used to translate Chinese characters into English/Romanized spellings -- it takes some time to learn as it is not very intuitive) in order to use a dictionary and other instruction books, and as a stepping stone to learning how to read & write Chinese characters (a massive undertaking in itself).