I haven't read the book and am not inspired to after watching the film. So taking the film as a work in itself, I thought it was mildly diverting (much like the salt path itself).
I enjoyed the scenery, but I loathe camping and the film reminded me why.
I thought the Jason Isaacs casting was great - from photos I see he looks very similar to the real Moth (and actually nothing like Simon Armitage, so I really didn't get that reference).
Agree that Gillian Anderson, usually so good, was a bit all over the place. I wish there had been less monosyllabic dialogue and more explanation.
The reason for them being in that situation was sketchy. Also, if they didn't really owe the debt and had the paperwork to prove it, but it was dismissed as being submitted too late - why on earth didn't they appeal?! Surely that is the next obvious course of action. Perhaps the book explains, but that was frustrating.
Also what was that underwater swimming scene?! Suddenly they're in the barrier reef or somesuch and what did they do with all their gear?
Fair play to the bunnies though. I am rural and we definitely have wild bunnies like this. It was very disconcerting when we first moved here and the dog caught one, I was convinced it had eaten Flopsy. But there are hundreds of the wild furry critters hopping around.