Aimsmum, yes, the 'thing' in the jungle - which could be inchoate because they all have their own ideas of what it's like - and all the other scary things.
Eg, the dr's big 'issue' psychologically is obviously his daddy, so daddy appears.
Maybe there's a huge pump in the middle of the island giving off hallucinatory vapour which makes their bugbears become real. Or maybe Freud has merged with God and is making it all happen.
I'm another one who's disappointed in it, I'm afraid, although I'll be interested to see what the big plot idea is. Hard to imagine how it can't be a comedown after all the hype, though. Still, I haven't quite brought myself to reading spoiler threads, so I guess I'm still half in there.