I started to watch this a few weeks ago as the "next" big project to watch after finishing X-Files that I never fully watched as I was a bit too young when it originally aired and only seen a few episodes in the later seasons.
I must say this has some resemblance to the X-Files but only in terms of the "monster of the week" episodes. I like that.
But this show lacks the ingenuity that X-Files has with the most of the time incredibly great scripts and the overall fantastic cast.

Nick, the Grimm (David Giuntoli) is a terrible, terrible miscast. I have watched the first two seasons now and I still really dislike that guy and still think another person would have been better for this role. So far, the show is greatly carried by Monroe (Silas Weir Mitchell), Rosalee (Bree Turner) and Captain Renard (Sasha Roiz).
It is said that the Grimm has some "powers" that make him who he is, additionally he is a Detective, making him, generally, somewhat smart figuring stuff out to solve cases. But when it is about Grimm stuff, he is stupid as f*ck for plot reasons only, even if they are obvious.
There's also this gimmick of his phone ringing, interrupting whatever he is just doing. This is probably the most annoying thing in this whole show, starting to seriously piss me off. This show pushes this really, really hard to a point, where you start to anticipate it in any kind of precarious situation that would solve plots right there if it wouldn't ring and in 9 out of 10 cases (felt) it does ring..

Just as unlikable as David is, so is Russell Hornsby (Hank) overstrained as an actor with his role as it seems. He is such a sterile cardboard character that I wouldn't mind if he gets killed off as cannonfodder at some point, there's no (believable) depth to his character at all.
The Juliette arc was awful as well, it held the complete show back in terms of progressing deeper into the Grimm story. The time that is put in here could have been better used when cut in third, the rest of the time put into more monster of the week episodes or to flesh out Hank's backstory.
The Juliette arc and Hank's arc to get to know the Grimm world were both overly dramatic and as I said for Juliette's part too much.
If you'd see someone change his appearance before your eyes after you shot him, you wouldn't go insane, you'd try hard to rationalize what you've seen. You'd think you're overworked, or tired. That the scenery played tricks on your eye or something. You might be shocked, at least for the moment, but you wouldn't start to become whiny as Hank did.

As a German the pronounciation of all the words could be improved immensely. I have to watch some episodes in German to see how they translate it or deal with it in general.
Can't be good, synchronization is terrible most of the time, the German voice of Rajesh ("The Indian Guy") from the Big Bang Theory is (yet?) borderline racist.
Some of the words seem to be very, *very* literal translations, like Glühenwolk[e]. "Glowing cloud", I assume, Glühen = Glowing, Wolke = Cloud but Glühenwolk[e] makes no sense, that's not proper German, correct would be "glühende Wolke". Glühenwolk[e] is like saying "glow cloud". They did this a couple of times with names.
There also seems to be only a single person on this show who tries to pronounce the German as correctly as possible most of the times: Monroe.
When he says more than a single word, he really tries and it shows - and pays off. He does a good job here.
Really lazy and almost bored seems David by doing so. He lacks passion in his job, he is so not trying because he doesn't care. As I said, miscast person.
There are some pet peeves that I have, aside some forgivable grammatical errors, though:
The pronounciation of Löwe or plural Löwen as it is used here. It is spelled like "lawn" just with an o as in "lown". Couldn't be more wrong. It's better to say "lowe" like "lo" and "we" as in whe[re].
Another word is Wesen, all creatures who are able to "vogue" or "woga", some word I can't identify. Wesen means creature or better: being. They say it like "Vessin".
And of course this woga thing. Still trying to figure out what they say here. There are probably more that annoy me but these three come to mind first.
You would assume they'd hire someone who speaks proper German for a show where German is such a centric part. But they apparently didn't, or took someone who had a German course in college but didn't do anything there.
That is somewhat disappointing.

Overall, this show has mixed qualities. Episodes are a complete up and down from week to week, depending on what the topic is but are usually - when good - only okayish, never really outstanding. There's no brilliance in this but it is able to entertain you, especially when Monroe and Rosalee have a good portion of appearance in the episodes.