As someone I know once said, and I'm paraphrasing because I don't remember the exact words: when playing Warhammer Fantasy Roleplaying you think you're playing D&D, but soon you discover that you're actually playing Call of Cthulhu.
As I've wandered quite far afield in my fantasy tastes in some ways, I do sometimes wish to return to The Lord of the Rings with some kind of twist. Even though the Warhammer setting is almost completely ridiculous in its recycling of over-used and even cliched fantasy elements, seeing them juxtaposed with a Lovecraftian undercurrent somehow just works and I like the setting a lot. It helps that the Black Library has a lot of good fiction in it too. I sometimes think maybe that I've wandered too far afield, and something a little more Warhammer-like wouldn't be fun to dabble in. Of course, that's part of why I have the slightly revised incipient MAMMOTH LORDS setting; which is more "Hyborian Age" than Lord of the Rings, but eh. Close enough.
That said, the idea of mixing a Lovecraftian tone onto high fantasy, or even evolved modern Sword & Sorcery seems difficult. What would these kinds of stories even look like?
Copied from an old post (geez, nearly ten years now) on how to adapt a Mythos-like tone to specifically D&D-like setting/game, I present for your enjoyment, a great example of what a SWORD & SANITY game might look like...
1. The Old Speech: Traders on strange vessels have arrived from faraway lands, speaking strange tongues. They're goods are odd, artistically, but nothing is dangerous about their cargoes. But the language they speak- it's hard to forget. People dealing with them pick it up quickly, and find its vocabulary replacing their own. They find themselves considering things to have darker, more malign implications than other. Sexual attraction becomes overwhelming desire for dominance and subjugation, students become mindlessly devoted to their now-cult leader like teachers, and so on. Soon they lose their ability to speak any other language, and start infecting others...friends, family, townsfolk, whoever. The PCs can be involved at any stage- hired as guards for merchants, assigned by the local rulers to investigate, infected and hoping for a cure, whatever. Eventually there will be riots as the infected descend into madness, becoming as the Old Ones. The traders depart for the next port, leaving chaos in their wake and taking with them the strongest of the infected.
2. The Sky: The PCs are underground, battling some cult or some evil underground race that already worships foul, blasphemous deities. Something alone the lines of Drow or whatnot. They discover an idol to said deity that leaves an impression in their minds- they start having strange dreams of a great eye moving behind clouds in the sky, a nameless terror of open spaces, etc. When they return to the surface they find themselves beset by a vision of the sky, one terrifying and ominous. Forced to flee for their sanity back underground, they'll have to search for source of this ancient evil in order to cure themselves of this Old One induced agoraphobia.
3. The Gates: The PCs discover, or are hired by those who have discovered, whatever the hook, two mystical portals that lead between two important locations in the campaign. However, travelling between these portals isn't something people can just describe- they never remember exactly what it was like, just that it was unpleasant and violating. The time it takes to travel between each portal varies, and some people come through with a bizarre, fatal sickness (i.e., radiation poisoning). At some point someone doesn't come through the other side, and the PCs have to go in to get them. Say an empire was trying to use the portals as a way to secretly move troops or spies into a rival empire, and their army never appeared on the other side. Something along those lines. (Or they arrived...changed)
4. The Strange High Castle in the Mist: Haunted Castle. Crazy old Witch lives between the dimensions within, drives residents mad or sucks them into her crazy multi-angled plane. I.e., it's Dreams in the Witch House, only in a castle, and probably with more stabbing of things with swords.
5. The City of the God: Decadent city in a wasteland. Fading power, evil nobility that exists only to gratify its monstrous urges...and the PCs are captured, or their beloved NPCs are capture, or the King's Daughter has been captured, or they're out to find this city to A. Enjoy its forbidden delights B. Steal something from it C. "rescue' someone who went to enjoy its forbidden delights...and may not want to leave, like the King's Evil Daughter, etc...
Anyway, somewhere in the city is a god trapped in a pit- not a Big Timey God, more like an overweight shoggoth with some spells or a lesser Old One. Anyway, like Conan, they probably have to stab it at some point to get away. Extra points if the city and its inhuman nobility are destroyed in a cataclysm as the PCs flee.
6. The Glove Cleaners (stolen from an Unspeakable Oath): Someone with access to a mythos tome and a printing press has decided to start scattering pages and excerpts from it all over the place. Never enough to assemble a whole spell, but just enough to unsettle those who read them and upset the delicate balance of the fragile or sensitive. Now the King's Daughter (i.e., insert Generic NPC In Distress) has gone mad after collecting too many of these fragments, and the PCs have to go hunt down the printer who is disseminating the forbidden knowledge. But he doesn't even know why he does it, just that he has the urge, and is otherwise a normal guy. (Probably protected secretly by a cult for your obligatory battle sequence) EDIT: Even better if you borrow from "Rome" and have it be mythos-themed graffiti against the local government or nobility.
7. The Disturbances: In the "Call of Cthulhu" short story, when the Big C stirred in his sleep as a result of Ry'leh's short rise to the surface, psychics, sensitives and artists all over the world went mad, had nightmares, or otherwise had a pretty bad couple of days. Now it's happening to the PC's homeland, continent, or to the King's Daughter. The PCs have to go and travel to the location of the not-awake-but-not-asleep GOO and stop its cultists from disturbing its slumber. They haven't woken it up, but they're causing it to thrash around a bit in its Forbidden Island/Underground/Remote Mountaintop/Ancient Ruin/Underwater Chasm/Vast Forest prison. That or it's not cultists but foolish archaelogists who happen to be mostly deep sleepers. Or...Dwarves. When in doubt, blame the dwarves...