Anyone tried the Zombie Invasion mod (I think that's the name)?
It gives you a holotape in game that can enable/disable the more hardcore aspects like headshots only and hordes/settlement attacks, but at it's baseline it makes all Ghouls slow and shambling like a Zombie but ups their durability by 9000% (may not be accurate
) and removes all armor from their head. They get increased spawns and ridiculously increased damage to make up for it.
It's really good, makes Ghouls harder as getting cornered is quite easy due to numbers and durability and on Survival every single Ghoul that's touched me has instantly put me in the kill animation where they bite your head off so it gets really tense. VATS builds will find them a cakewalk but I personally only use VATS to scout out enemies (enhanced Raiders and Gunners mods get very hairy) so going in Rick Grimes style with the DLC revolver feels so. damn. good.
I'd recommend giving it a look, along with Raiders & Gunners of the Commonwealth. The Wet Work Specialists (Gunners) and Raider Juggernauts are quite something.
There's also a mod I've found that is ridiculous but will be a great end or post game challenge; 'Elite Bosses' or something like that, it adds 40 bosses throughout the game that have up to 40,000HP. The DeathClaw Matriarch in Boston is painful, tried running from it and only got about 6ft before she grabbed me in that crazy stomach stabbing kill animation, sucked but it made going through that place tense.