As expected, 666 Park Avenue is a very soft horror show, you rather sit and wait to be scared than actually get frightened by what happens on the screen. It is obviously made for women with Jane being a more significant character than Henry. In fact, Henry's position is very weak, I felt like he did not add so much to the story, even though Gavin says that Jane is how they get Henry. I don't know what the Dorans see in him but Henry's importance might later increase.
The residents of Drake are dying or get hurt one after another, so if hey keep up like that, it's likely that the building gets empty very fast. Four victims, out of which two complete deaths, plus one died for the second time already and one is still said to be alive but in hospital. Impressive.
Then, in my opinion, they gave away too much now (in AHS even now that the first season's over, we still don't know why the dead couldn't get out of the house). The only big secret now is who Gavin really is and how he got this building and this power. It's unlikely at this point that he makes these deals on his own, there must be some greater evil he caters to. But other than that, all is clear: you get to the building, you're seduced by something your soul desires and then you pay a high price for this.This is what Jane and Henry will go through, and the little secret is what will seduce them.
There was a number of things that will most probably have some development in the future. We will learn something about why the door in the basement/laundry room was sealed (a gate to hell?), what happens when Henry's employer finds out about him talking to Stone, Gavin probably intentionally took Stone's spot to get the two meet. Finally, the red dress must have some symbolic or maybe even very important meaning as we see at least two instances where Jane wears the red dress.
So far I could not sympathize with any of the characters, they are mostly annoying. Jane is way to noisy and ambitious, Henry seems a little uninsightful and full of flat jokes, Gavin is too evil and Olivia is too cold, neither of them show much humanity.
It's watchable, I especially recommend it for middle aged women missing some thrill in life, men are unlikely to enjoy it and teenagers probably have better things to do than watching it. But AHS was way better.