late to the party, but finished this last night. absolutely superb stuff, and on a par with anything out of the USA this year, and that includes true detective etc. funny, bleak and brutal, sometimes all at the same time. lancashire and pemberton deserve every award going.
i agree about the one flaw being right at the end with the out-of-characterness of that decision on catherine's part, but it's not a big enough point to ruin what is otherwise a stunning piece of television.
oh, and the theme music was awful, completely wrong choice for the show, but i can forgive that too.
all that said, i really hope there isn't a second series.