I really enjoyed this (but I also did in London). I don't know how many changes they made to American-ize it but it was definitely essentially the same play (there was a conversation about the healthcare system that I don't think would've worked as well in the UK so I assume that was different). Sound design was great, and that first jump scare really got a lot of people, though later ones didn't quite have the same effect (I think some of the later screams weren't quite as loud/piercing as the theater in London? It at least made it slightly more credible to what they were supposed to be as opposed to just a cheap scare tactic).
The acting was fantastic on all levels, and it was nice to be able to see it again to pick up on the clues leading to the ending. Based on some timely gasps in the audience, I think some of the other audience members were able to figure it out before the end as well, and my friend definitely knew something was up with one specific character but she didn't know what exactly. It's definitely a show that benefits from seeing it live with an audience, as hearing the audience reactions is half the fun.
I do agree that Ben's character was a little uneven and seemed to function more as a plot device than anything--I would've also appreciated more depth into the gentrification conversation. But otherwise I think the play is a fantastic thriller. It's not meant to necessarily have a ton of overarching themes, but it's really just there for you to experience it. The conversation that the characters have while waiting for 2:22am are really just a bonus and I found them overall enjoyable to watch as the night devolved. There were a lot of smart touches in both the script and staging that just really helped set the mood.
The only thing is (as others have mentioned), the Ahmanson is big, bigger than I remembered it being. I had thought the last row of the orchestra still felt pretty close, but being used to Broadway theaters now, even row T felt far away (though my friend was amazed at how close it felt). And I remember the mezzanine feeling rather distant, not to mention the balcony, so I can't say how the show played from up there, as it's a show where you do need to get kind of invested in its characters.