I love Once Upon a Time. I love fairy tales and fantasy settings and True Love's Kiss and happy endings and a touch of bittersweet is just fine too, and the balance between the fairy tale setting and the mundane world in this show is done ever so precisely. If there were any less of the fairy tale setting I'd be chafing for more, but I would dare to say the balance is just right, like Goldilocks's porridge. Did you like The 10th Kingdom? If so definitely check this out; it has quite a similar feel. And I just read an article in Entertainment Weekly that says it's "TV's highest-rated new drama among adults." Lot of qualifiers there but I hope that means the ratings will keep it going. Yay!
Grimm, on the other hand, is well-done but I don't love it. I'll watch it a little more of it but it's, well, grim, so you can't complain it misrepresents itself. It's clever and manages to go places I didn't expect but it's horror, not so much fantasy. (It gives me the same vibes I used to have when the Datlow/Windling anthology of The Year's Best Fantasy was first published and half the stories were horror and I was jumping out of my skin every other story, yelling, "This is Fantasy?" at the thing. Some years later it renamed itself The Year's Best Fantasy and Horror and I said, "Thank you, cripes!") Y'got your police procedural, y'got your serial killers...nothing wrong with that if you like that kind of thing, but I could go for a little more True Love's Kiss sweetness. Those of you who like Supernatural should give this a look. (And the horror element is exactly why I bailed on Supernatural, too.)