Just did all of Howl O Scream (minus the shows) in 3 hours or so. My thoughts from someone who only has done HHN for the last 7 years:
Pros:
The scares we got in the houses felt more organic as there are no barricades and they can get close to you. Also the pacing felt great where we could get at least 85% of the scares, although this can be attributed to how empty the park was.
Scare Zones felt actually scary and less of a photo op for guests to take selfies. The roaming haunts were a nice touch as well and were able to hide well too really scare some. Feels like they had more freedom to try different things to scare people. One person literally climbed through a hedge to get me while I was sitting down. Again this could be helped by how empty the park is compared to HHN.
I liked some of the shirts (and they aren't all black!)
The bars felt like a party atmosphere with "cage dancers" and people in costume. If I was planning on drinking, I would've enjoyed spending time there.
Cons:
Production, or lack thereof. Set designs, facades and costumes all look like they came from Spirit Halloween. If I only saw pictures, I would've assumed it was a local haunt and not a major theme park.
Overall lack of information regarding wait times and directions to the next location. This was my first time actually at SeaWorld and it wasn't exactly clear which way to go unless you were looking at a map. This is only a minor gripe though.
Only 4 houses and 4 scarezones, along with 2 shows, is a hard sell when compared to HHN. The houses are fairly short as well
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Overall, it's a fairly decent experience considering it's the second night of the first year. We probably won't go back for the remaining of this season, but will check it out in 2022.