Darkest Dungeon is a tough and well-designed dungeon crawler that tests your ability to manage resources while dungeon crawling and managing how you invest in the local hamlet upgrades. The premise is that you inherit your ancestor's manor and now must deal with the eldritch forces he meddled with in the past. General gameplay: advancing in teams of four, your heroes move left to right, dealing with enemies, artifacts found within dungeons called curios, and building up towards each boss of the relevant area. Each hero has a range of abilities you can unlock and upgrade - switching them outside of battle as necessary - and improving their equipment for better stats. The heroes' ranks do not reflect their overall stats but their "resolve" and will be able to take on higher rank quests. Combat: Turn-based, RNG based combat is the meat of Darkest Dungeon and it can get frustrating because well-planned runs can go awry due to a few bad rolls. That being said, you can definitely give yourself an edge using trinkets to improve stats and rolls, and picking heroes and abilities to adapt to the enemies that you know will appear in a given dungeon, e.g., don't bring bleed abilities to the cove because blight's more effective there. The game itself is not difficult to play, the rules are simple and all town upgrades are permanent so unless you're on the highest difficulty (has a time limit to finish the game), the game doesn't actually have a fail state. Everything in town costs money or resources EXCEPT the heroes - they continually turn up in the hopes of gaining treasure and glory. So even if you lose everyone, at least 4 more will appear, then you just have to send them out to get some gold and reestablish yourself. You must learn to accept your losses and try again.
