So, a "classic custom" server started up back in 2004 or so called Winter's Roar. It's known as Shards of Dalaya now, and 10 years later it's not very classic since raid gear has inflated to nearly the stats of live.
Anyways, this server is completely custom with its own lore, gods, etc. Part of the lore involved Rivervale getting totally fucked by the main evil dude (some Iksar, can't remember his name atm). He infects parts of the world with "the mist" or whatever.
Anyways, Rivervale eventually got infected with this shit. I was one of the first people to explore the zone after it got updated, and it was one of the most memorable MMO experiences I've ever had. Essentially, the entire town is haunted. There's a couple quest lines there, and talking to the NPCs alone is creepy enough, not to mention when you finally make it inside the druid guild to find the cannibalistic halflings...
Basically, haunted Rivervale > classic Rivervale. That shit was awesome.
Edit: If you're curious,
http://wiki.shardsofdalaya.com/index.php/Rivervale. Still doesn't do justice to how creepy experiencing this zone is.
Hopefully linking SoD stuff here is okay. I'm not really recommending the server over P99 since I think it has some serious issues that have been neglected over the years (inflation and the raid scene makes it nearly impossible for new players to get into).