I wasn't certain what to expect when I started watching the opening season of Downton Abbey, but somewhere around the second or third episode, I got hooked. After that first day, I "marathoned" all three seasons in order to catch up.
To me, this is basically a prime-time Soap Opera with continuing storylines, featuring high drama, some comedic lightness, and terrific acting. It's definitely not satirical or tongue-in-cheek (like Desperate Housewives) or overly campy and unbelievable (like Dynasty), but more of a Knots Landing (the best nighttime soap ever!) set in the world of Upstairs, Downstairs, meaning enjoyable stories, a talented ensemble cast, believable characters you care about, and a fascinating historical setting. The locations and sets and costumes are outstanding as well, and the whole series is produced with a top-notch level of quality that only British TV can muster. Although Maggie Smith is a standout among the cast, stealing every scene in which she appears (due, mostly, to her laugh-out-loud one-liners), she's completely surrounded by actors who can easily handle the chore of delivering the own goods each and every episode.
You'll laugh, you'll cry, you'll be on the edge of your seat for many of the storylines. Overall, an excellent show thus far! Bully to the Brits for creating such a great series! I can't wait for Season Four!