I did the Marathon this year; I can assure you that the 'not too testing' hills seem pretty big on the second lap. The disused railway line is also longer second lap- not just because you are tired, but also because the second lap actually takes a slightly different route and joins the track further out.
All in all an enjoyable run in a rural setting, well organised an excellent value for money. I won't be back there next year, but only because I managed to squeeze in under 3h15m, so I've got a guaranteed place in London.