I agree with the comments above, it is difficult to point at which role would be the most critical for a project manager. If I were to take a guess, I assume that creating the story behind the product line. As Andrew mentioned earlier, their are great and innovative products out there but don’t have a story. In addition, from my experience, the products that I work with have huge stories that revolve around them and their importance within development to manufacturing. It is important for the PM to utilize to story of the product to consumers are influenced to purchase it.

Chris