the Demo is quite enjoyable, I already noticed differences, for one vocals are tougher to nail, and double peddle drumming leaves you more sore than........well too many youngens so I'll refrain on that analogy..
but so far play wise it's got some differences " though I believe it was in game informer I read that the updated system for GH:M will also contain a patch for GH:WT..but don't quote me on that just yet..
most of all though If you enjoy Metallica " more importantly there older work, and many of the bands surrounding them" then I would say it's a good grab...
I'm still holding my breath for more DLC of Tools older stuff from undertow, or Ænima