yes I've read the dark is rising loved the Dark is rising story especially, as you said very atmospheric I remember feeling cold just reading it very Fumbulwinter (excuse spelling) Sadly the film is pretty rubbish.
Not sure if Ragnarok is coming or has occurred yet. Quite like the Idea that the pcs are part of bringing the new age about( see Runemarks by Joanna Harris for this idea.currently 're reading at moment it it's set 500 years after Ragnarok ) this might explain why a disguised Giant lives amongst humans as a Blacksmith, all type's come to him for equipment, weapons etc so he can pick up on rumours of bringers of a new age and omens there of too, and also why he has an odd mix of apprentices. As old one eye says in Runemarks there have been many beginnings and many endings this is but the latest one.
As a complete aside, another potential Zed spell going wrong could result in the events that occur in The MadCap laughs a3 part adventure WD did for Stormbringer/ Hawkmoon the main villain could be the Riddling Reaver or Loki
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The fun with the Zombie apocalypse we are currently playing as my group play themselves so no super powers or magic weapons to hide behind unless you count my own Medieval reenactment gear (very rusty but non magical as far as I know or my wife's startling ability to kill Zombies in the game with a Hand scythe from our garden shed and a big Toyota Hilux theft tends tomangle any zombie that gets in the way.
Another book in the system actually allows you to play through a Ragnarok scenario.
It may take months or years, but eventually I will do it! 
I've already got a queue of stuff to convert for now with the UK modules.