Just from the descriptions of the series, I had Grimm
pegged as a "cop show with sci fi window dressing" long before it premiered. (Around this time last year - when all the fall shows are being pitched and promoted in clips.) With a cop as the lead, that's the dead giveaway. So I was suspicious from the start whether it would ever become more than just that.
The premiere established the mythology and after that, went too heavy on the cop show elements. The creators didn't suddenly change their mind about the type of show they were making after one episode, they just doled out the elements in different proportions over time. One good episode isn't enough to keep me watching a show, especially if it looks like its wandering off in a direction I don't like. But if it comes back to the proportion that suits me, then I'll stick with it.
Contrast that with Alcatraz,
which also promised a possibly interesting mythology but then depended too heavily on procedural elements. In that case, my patience was not rewarded. Hence my suspicion about any series that looks like the dreaded cop show with sci fi window dressing. I've been burned too often to trust that sort of show.
is an unusual example of a show that gets the proportions right. I'm sure they'll bring back the cop show stuff next year, because the purpose of that stuff is to provide padding and get them to 22 episodes or whatever per year. That need will never go away.