A good whitepaper should be concise. It should clearly reveal the problem its trying to solve and why their solutions works in believable terms.
I would not say so. A good whitepaper for me at least is something that explains the current problems at hand along with the solutions that the startup is going to provide in order to combat those problems.
However an extremely technical whitepaper is generally a no - no for me. I get turned down by too much of technical jargon and most whitepapers try to keep it to a minimum otherwise there is a separate "technical whitepaper".
However a badly written whitepaper or a rushed whitepaper is a bad mark for the project.
I believe a good whitepaper states their aim or goal. They have to state the problem and come up with a good solution to convince investors to invest in their projects. It also has to be realistic and not just for the show.