They split the first series in the US, first 10 episodes shown up to the end of November and it's only just resumed. I've quite enjoyed it, though it's not mind blowing, but worry it may go the way of Flash Forward and so many other sci-fi shows of its type (which have been better) and get axed before the real mystery is revealed and resolved, though they do reveal quite a lot by the end of the first 10 episodes. There are a few stupid moments.
It started off quite weakly in the ratings war, though it has picked up a bit, but in the trigger happy world of US tv, I'm not overly hopeful of it getting a second season.
I also hope they don't do what thery did with V, because they split it like that and called the first half of the series season 1 when released on DVD and the second half season 2.
Apparently NBC created a series of "prequel" webisodes which aired from 25th of Feb on NBC.com. I've not watched them or found them yet, but I think they'll also end up as an extra on the DVD box set.