The premise is that Our Hero (a detective in the lovely and lushily-filmed city of Portland, wow) finds out that he is actually a "Grimm"-- that is, a person who has the ability to see various (often hostile) supernatural creatures in their true form-- which means that he has a responsibility to stop them if necessary (why, yes, some of the folks working on this show DID work on "Buffy the Vampire Slayer"; why do you ask?). It does really fun things with "traditional" fairy-tale ideas and folklore, but isn't slavishly dependent on it. The world-building, so far, is doing nicely complicated things (or at least setting them up), with longer-running story arcs mixed with monster-of-the-week cases.
*The Girlfriend character is sometimes a bit annoying, mostly because she isn't getting very much character development-- OTOH, the show is focusing on cop work and detective cases, and she is a vet, so there hasn't been a lot of space for her to get directly involved. However, I reserve the right to be extremely annoyed if she keeps being such a cipher/standard "I don't even know you anymore since you started getting so annoyingly dedicated to your job! *flounce*" characters. I have hopes, however, that whatever direction she goes in, it will be more interesting than that. Also? Everybody else? EXCEEDINGLY COOL.