Think "Clive Barker writes North Korea"
At least the scary bits are.
But I don't think the Umbral Court has a need for so much overt villainy. Zon Kuthon is upheld as the savior of the people. But its not like the shadows are walking in the sun. It's not like there's mass rallies for Zon Kuthon - maybe the oddly timed celebration in reverence of some cryptic astrological phenomenon, maybe there are some rather... violent ceremonies. But it's not an occultic terrordome of EVILZ (at least not openly). Zon Kuthon and his church is more weird than evil, imho.
I think Nidal is more the place where people just... disappear. There's nothing overtly menacing about most of the country, most of the time. But you know. Farmers gotta farm, sailors gotta sail, masons gotta lay bricks. People live ordinary lives. But they know. It's probably a fairly normal place most of the time, indistinguishable from rustic Taldor or Andoran. But... you know.
Heck, in Giantslayer, the players can travel to shadowy Pangolais for supplies and refits. It's not like even the heart of darkness is unwelcoming.
I haven't read the novel, but that's just my take on things from the Campaign Setting. Nidal is evil, but its masters have no need to be obtuse about it. They use scalpels, not cleavers.