I am not a fan of TV series, just don't see the point, and I typically filter them out of my Amazon/Netflix/iTunes subscriptions. But I happen to live where Grimm is filmed, and they did several episodes in/around my office using coworkers as extras...which sparked my curiosity.
When one season popped up on Amazon Prime, I tried the opener just to see what it was all about. Then I watched another...and by the end of the day I'd gone through the entire season and purchased the next. This stuff's like peanuts--you get hooked on the whole alternate world with fairytale creatures in disguise bit, and a lot of the fun is seeing what other critters the writers can dream up.
Incredible storylines? Not really--they alternate between obvious and really straining credulity (although given the subject matter I'm not sure any fan would really care). But the cast is skilled and likeable, especially the supporting roles, the makeup and special effects very inventive, it's in a city that may have invented weird so it fits right in, and I find myself downtown, looking for that little herb shop.