The last time I did this was with Arrested Development, and for the same reason. It didn't look like anything I was interested in when the first season aired, but on strong word of mouth I started watching during season two. I immediately fell in love and gobbled up the entire first season on DVD the first chance I had.
I hesitate to compare Modern Family to Arrested Development because they're apples and oranges, but I do think they're both brilliant. The threads they share are an amazing cast and strong, sharp writing. Shows like this--intelligent, multilayered, well acted--put other ratings powerhouses like Two and a Half Men to shame.
My favorite branches of the Pritchett-Dunphy family tree change with each episode. Sometimes (often, really) it's Mitchell and Cameron, sometimes it's Phil and Claire, and sometimes it's Jay, Gloria, and Manny--but always it's Luke. Always. Luke. Nolan Gould just may be the best child actor in comedy right now. His timing and delivery are impeccable.
The TV Nerd proclaims Modern Family a new favorite, on par with 30 Rock for sheer consistent genius. Catch it if you aren't already. It just might hook you too.