I watched the pilot episode on DVR, not expecting to be impressed, but... I liked it. Enough to keep watching for now, at least.
It was very, very derivative of Buffy... the Chosen One in every generation, destined to fight the monsters, with the older mentor figure who arrives to tell him about his destiny. He doesn't seem to get any Slayer-like superpowers, except the ability to see through the monsters' human disguises, but the monsters seem to be easier to kill in Grimm than in Buffy/Angel... you just shoot them a bunch of times and they die. Which kind of makes me wonder why Aunt Marie had that Angel-like cabinet full of medieval weapons.
I expected Nick's finacee to be dead by the end of the hour, and was pleased that they avoided that cliche. I expect she will probably play the Joyce role in this show, trying to make him turn away from his destiny and have a normal life. I'm guessing she'll probably end up as a member of his "Scooby gang" along with his partner Hank and the reformed Big Bad Wolf.
Depending on the quality of writers this show gets, it could be good. The pilot did surprisingly well... 6.5 million viewers in the Friday Night Death Slot, opposite Game 7 of the World Series, on the #4 network.