Colin Firth reminds us of his extensive talent here, perfectly depicting the dichotomy of a grieving widower who must keep going for the sake of his two daughters. He is ably supported by the two young leads, at different stages in their lives, displaying their confusion, grief and alienation (both physical, having moved to a strange country, and psychological, as they come to terms with their new reality as motherless children) in age-appropriate ways - and very convincingly. The added dimension of the guilt felt by the younger daughter is believable and tragic.
All in all, I am surprised by the number of negative reviews this film has received. I think Michael Winterbottom was seeking to depict a slice of everyday life, albeit very bitter-sweet and raw. Maybe there isn't a huge amount of action, but most people's lives tend to be that way, and action was obviously not the motivation behind this piece.
Personally, I thought it was excellent and would watch again.