Yeah, it's been a good show, or at least fun to watch. I'll hate to see it end, but even if it were to have continued, I fear that it might have started getting worse as they tried to meander their way through unrelated stories. Kind of like Doctor Who could do after x years, where the actors from week-to-week go "oh look, there's a Dalek, surprise."
In my honest opinion, the known end-date for Grimm (as opposed to those series that just never get renewed) at least gives the writers a chance to wrap up the story in an epic way. Whether they will, or they'll "pull a Lost" has yet to be seen.
Wayne