I don't think it's that they're implausible... they're just not as good as CSI, Criminal Minds, NCIS, etc. They've really focused a lot on the two main characters, pushed Grace Park aside, and pushed Daniel Dae Kim WAY in the background (not that he cares, he gets to stay in Hawaii another year to work.
I think if they put as much effort into the cases as they did the McGarrett/Danno interaction, this would be a great show. There's only been one episode that I thought was truly great, but it's a very watchable show though. It probably will play better on DVD.