During the war between Bael Turath and Arkhosia, a plucky daddy-dragon named Arantor decides to take his daughter (Imrissa) on a raid. What better way for a father to bond with his only child: slaughter! They'd learned about a fairly remote Turathi outpost in the jungle, and being magical-flying-lizards figure that it should pose little hindrance to themselves. As their strafing away, flash-freezing hapless tieflings left and right, they're surprised to find out that its not an outpost, but a refugee camp.
Realizing their cockup, they fall back into the clouds to decide what should they do: report their mistake, or just cover it up. Well, they didnt agree, got into a fight, and eventually Arantor was put down and woke up in the Shadowfell as the new owner of a bleak and gloomy domain...which reflected the fortress and camp that he initially destroyed mostly be accident.
The best part? His body rots away over the years in his domain until all thats left is a dracolich-like form, except his daugher's skeleton is stuck inside his rib-cage and it whispers the names of the innocent people he'd killed oh-so-long ago.
Monadhan is unfriendlier than most domains, which I suppose doesnt say much. As the name implies its where traitors go: generals who lead troops off to die, or greedy people who sacrificed others for personal gain. Basically the more of a backstabbing asshole you are, the more likely you'll end up here.
Of course, its not just the citizens you got to watch out for (though the fact that Kas lives here doesnt help matters much), as the mists surrounding Monadhan sometimes crap out random encounters, and the river is filled with "parasitic fish", primordial hydras, and chuul juggernauts. This is some fucking lethal beachfront property. The jungle isnt much safer, as its filled with massive insects, snakes, and toxic plantlife.
Arantor himself is a level 25 solo brute that gets a static initiative roll of 30 and 20, for Arantor's and Imrissa's actions respectively. They each have their own nifty things that they can do, though Imrissa is stuck inside and uses influental whispers to deal psychic damage with a domination effect or dead dragon's stride to give Arantor a free teleport. I think its really cool that when you kill Arantor that he busts open and Imrissa escapes to keep up the good fight.
Getting into Moradhan is half the fun (the other half being to get the fuck out). A sidebar on page 15 gives you four examples to entrap a party within the mists, and the article also provides two specific ways to escape Moradhan. One is easy once you figure out how, but there's also a way to dissolve the domain entirely in case your party likes to be thorough.
I actually like that they arent keeping the whole thing secret from everyone-including-the-DM. I dont recall ant Ravenloft products spilling the beans on much, requiring the DM to determine how/if one could escape the Domains of Dread or remove an individual domain. Obviously you dont have to use either method, but its great for the DM on a time budget (which is why I, in part, subscribed to Dragon in the first place). Its certainly a step up from the, "figure it out yourself," department.
I found the backstory interesting enough to maintain interest throughout most of the article. A good way to tie in a dragon fight without making it too cliche. Its a lot like a self-contained adventure without the formatting and a more mutable structure: you get a village to start things, hooks to draw them out, and a way to resolve the whole thing.
I didnt find a level recommendation, but judging from the skill challenge and Arantor's own level, I would say that no party below level 22 should try taking this place down.