Fallout Equestria
Yes it IS Dark, it can get very VERY Dark, but never, at ANY point does it come even close to being Grimdark. no matter how dark it gets, how much bad happenes, it never loses itself TO darkness. The story, overall is about HOPE. That even in the drakest, grimmest, most hopeless seeming times, all it takes is one small spark of hope, to ignite a fire and burn back the darkness. To help rebuild what was lost, to give the ponies hope that they CAN make the Wasteland into the paradise it once was. Simply by never giving up, never giving into the darkness, never accepting it as "the way things are"
No, instead saying "this is NOT right" "This is NOT how things should be" and doing everything they can to fix it, to drive back the gloom, darkness and suffering. FOE is the very antithesis of Grimdark. And, yes it is a very YMMV story, but, IMO, it diserves a chance and is MORE then diserving of all the praise it's gotten and it's popularity. The Fallout parts are explained well, you DON'T need to know about them, though it does shed some more light on what's going on, as well as building up a bit more suspense when you hear about places like maripony, or The Enclave.
Yes, as you can tell, I cannot recommend trying it enough. Yes it is Dark, but never grimdark. With but one or two possible exceptions, the darkness is never gratuitous. It is there to serve the story, and works. And as to Gore, really ther is very little. AFTER chapter 3. Seriously chapter three is the worst, but, for a reason. it's the big shock to the reader and to Li'lpip. Showing just HOW BAD the Wastes are. but, after that, it never goes that detailed or that bad again. it's there to let kkat AVOID going that gory or that dark. Showing one really bad scene early, so the rest of the story, they can simply hint, allude, or very simplistically describe things, and let the reader fill in the details without having to give them
So yes, keeping in mind chapter 3....or was it 4? one of those two. Is the absolute worst it will get, and the rest is much easier. Give it a try.