This series does not have a thread, but I think it deserves one.
First: "Grimm" was accused of being a Supernatural Rip-Off. I will not deny there are certain similarities, and maybe Grimm would not even have been made without Supernatural. Yet, the show still got it's own character, and even manages to avoid mistakes Supernatural has been subjected to.
Short plot synopsis:
Police Detective Nick Burhardt finds out he is a Grimm. A human being capable of seeing a "Wesen"'s true form. Wesen could be decribed as some kind of Were-Creatures. Appearing human, until they want their true self to be seen. While the Grimms are capable of seeing their true form, and have been hunting them down (as many Wesens are not too kind towards human beings when given the opportunity). Many of those Wesens were the source for fairy tales (many written by the Brothers Grimm, therefor obviously the name
- Supernatural was accused of focusing too much on the Sam/Dean bromance, while other characters often die a quick death. So, it took Supernatural a while to establish at least some decent recurring cast.
- Grimm did better that way. Nick Burhardt got a Police Partner, his superior in the PD, a Blutbad (Some kind of Big Bad Wolf) friend, and a girlfriend. Which enables some nice constellations:
1) His Police Partner Hank Griffin serves when doing ordinary police investigations
2) Hank Monroe (the Blutbad) does basically the same, but comes into play when the Wesen world is involved
3) Having seen Supernatural, I somehow expected his GF would also die quickly, to give the character a personal loss and bitterness. Fortunately, she survived. Her character added some nice (often tongue in cheek) "Superheroes secret identity he has to KEEP secret" theme.
All in all, the regulars allow more variety in interaction than in Supernatural. Yet, it comes at a price. Nick suffers a bit from (what I like to call) "Luke Skywalker Syndrome". Means: The hero has little allowances to go over the top, and remains somewhat generic. While the interesting stuff has to be performed by the supporting cast.
Supernatural's Sam and Dean are certainly the more interesting and characteristic protagonists. While Nick is not a too compelling lead, that weakness is compensation by a larger group of supporting chars.
Grimm's overall setting mostly keeps close to the classical detective/crime story. The adversaries also usually meet on more equal terms. Even when a Wesen is far more powerful than a human, a gunshot is usually enough to take everyone down. Which allows the Grimm stories a more direct, spot on approach. Though sometimes -with Nick being a cop, and having a complete PD as backup- he might come off a tad too strong, with too many ressources.
All in all:
The series certainly drew quite some inspiration from Supernatural. Yet, it also manages to uphold a unique character. So, if you like Supernatural, and you do not mind that another goes a similar direction, you should give it a try.