I thought the other day - one of the few themes that they haven't yet explored in any of their Halloween attractions is this Mexican Day of the Dead type theme.
As
Taypru said, the one at Port Adventura works pretty well, although I do think this theme is more suited to a family audience, so I think Alton have got it spot on.
RE that music ad the start of the advert, what song melody is that inspired by? It's probably a custom made piece, but it sounds like they've used the middle portion of the Duel LIVE theme (back from '08) as a bit of influence or is it something else?
Finally, RE the real frights, I really hope the new maze isn't Phalanx-related. I know it's hard to devise new concepts especially when they've covered most of them, but Phalanx is a bit meh IMO. I'd much rather see something Th13teen or Curse-related, but taking it up a notch. If it is Phalanx, I really hope they re-introduce the "splitting up" concept last seen in Sub Species.
On a side note, and I know people say this, but I genuinely had three trips lined up for Scarefest with three different groups, but I cancelled one after it was revealed that there's only one new attraction. I'll probably knock a second one on the head if it is Phalanx-themed, me and my friends want to see something supernatural / genuinely scary / push the boundaries, it's just not worth multiple visits.