I found the unique benefit to Pimsleur to be the challenge/response
way of trying to get you to recall phrases.
If you are studying on your own and have no one to speak to, it is
one step closer to a conversation then you get with a traditional audio tape.
However, you are much better off having a conversation partner.
Also, Pimlseur suffers, as others have noted, but not providing grammar
explanations, writing, etc, etc. so it can only be a modest supplement
to a more complete effort to learn the language.
Finally, I found it a great way to fill time during my 45 minute drive to work,
when working out of a regular book would have been... difficult.