I'm a Hollywood guy, but I've been to Orlando's HHN twice. To me, it boils down to two key factors: set design and scareactors. Orlando is undoubtly the best in set desgin, with no black walls in sight unless it's an intentional effect. But Hollywood is much better with scareactors... they're so aggressive, relentless, and in your face way more than Orlando, where the quality is very uneven.
But there's a third factor: the crowd. I personally find the crowd at Hollywood way more engaged with the spirit of the event. There's a very genuine and enthusiastic following for haunts and horror, and I'd say easily 25% or more of the crowds are wearing some sort of horror or Halloween apparel, many of it very clever and original. In Orlando, I saw that level of enthusiasm for Bill & Ted, but not really anywhere else. In Orlando, the energy is more about the HHN event itself (Did you go last yeat? What's your favorite icon?), while Hollywood is more about Halloween, horror, and Hollywood as a whole.
Getting back to how HHN could be pulled off, I do remember that many years ago, Frightdome in Las Vegas ran its mazes in small groups where you followed a guide. If HHN did similar, they could limit and exactly know where other groups are in the house, and could better pace crowd flow. Although one true story: while admiring a set design, I unintentionally fell behind and accidentally went down a wrong turn, where I discovered some scareactors in a break room smoking. One of them just looked up at me and calmly said, "You were supposed to turn left."
