Games have 3 stages: early, middle, and late game. Early game is the "you always start here" part until you get to "you can do your normal stuff." Late game is: "You've done everything, now the game will cycle in x manner until it ends." Mid game is the parts between the two.
A game can withstand one of these being bad. Just ignore that part and 'sit' in the other two. If two of them are bad, however, the game itself is bad. The below is what I can recite after playing about 300 hours of a game. Really, I can just play the game mentally now. I don't even need to fire up the program anymore. I just know on my own how everything "goes."
Darkest Dungeon is full of reports where players say, demonstrate, and prove that they are doing everything right and still getting screwed in the early game. Screwed here means "suffer until you get lucky and aren't screwed anymore" or "well, I suppose you could just stop playing"
I've yet to see more than a few reports on what the game looks like in late game. The answer is: it's even more swingy than the start. Therefore its almost bad. Here's the way a typical late-game run looks like:
1) You have a mix of 6,5th 4th,3rd and a few 2nd,1st level characters.
2) You have a bunch of carefully chosen trinkets from battles (you don't waste money buying them).
3) All of your used buildings are fully upgraded and you have about around hundred of each heirloom just piling up.
4) Either all of your characters skills/attack&def unupgraded and you have between 40-100k, or you have them all upgraded but you are sitting on 7-30k.
5) Either you just refuse to fix your heroes and you have the upper range of that money, or you fix just the necessary things and you are in the middle, or you fix everything and you are at the bottom range.
6) Either you chose missions that look like the best risk/reward between the crappy ones that fill up your items slots or the good ones that let you just explore for a great trinket.
7) Either you dismiss heroes who don't fit your perfect line-up causing at least 3x the grinding, or you take whoever fits into a mostly cohesive group. We'll be assuming middle-of-the-road groups. Otherwise you'll spend a lot of time simply not being able to take
any missions (an average of 3-4 per tier) because you don't have the perfect group available. Basically you're forced to either abuse the retreat mechanics with a noob tier group (which the designers hate and are constantly trying to patch) or you play the game in a compromised, realistic manner.
8) Either you equip your best trinkets to have the best chance of winning said mission or send them out to fail. It's still your choice but we'll see later why this is a damned if you do or damned if you don't scenario. Equipping your middle of the road trinkets is essentially the worst of both worlds.
9) You can either buy all the supplies you need or you can hold back. If you buy what you need you'll need 6-7k just to ante up. If you go in without shovels/food/ a torch, you'll starve/stress/shambler TPK after the first fight. The 6k minimum is the "lose condition" in the game.
10) You go through the mission a bit. You can either run like a coward before things get hard or after. If you run away before you do fighting you have no loot. By running away before things get hard, you make the game about 12x longer/more grindy than normal. I suppose we could test this strategy with a person overseeing a lua script ... but even I don't have the patience for that. We'll assume you go until things get hard.
11) Things get hard because you get no loot (3 empty sacks in a row) if you keep up full light. If you want full light you spend an extra 3k in torches effectively throwing away the completion bonus and you raise the "loss condition" up to a whopping 10k gold. You will break one of the above conditions if you need to hold 10k. So either you lose/risk loss early, or you continue via the below.
12) Once things are hard for your fully decked out/fully invested/fully supplied characters, you can do one of two things: run full throttle into a TPK, or get stabbed in the back by a TPK. Said TPK is only avoidable in mid game because you can "outlevel" your competition but not in late game.
Here's an example: straight a jester 5, arbelest 6, gravedigger 5, lycanthrope 5 want to get a decent item. There were no other acceptable missions and they are running everything the best they ever will. The jester's 15stress doesn't keep up with the 25-30 stress per person per fight. Even with straight stress heals at camp, once one character breaks you have to finish the fight. Once one character breaks they all will at successive fights. The only way to tip the scales would be to run two jesters ... which you can't due to the fact that the stress heal only works in position 4. I have a lot of experience with stress healing because i have TWO jesters at every tier. Just trust me that after 200 hours of gameplay, this will happen at champion missions.
So your characters have become misbehaving pokemon. Despite optimizing speed, two tough enemies got the jump on one 75% hp (it's not realistic to maintain 100% heals on all characters) enemy and he dies. Now you can have two options. Fight to retrieve his trinkets, or click the retreat button. Let's explore what happens in each scenario:
"If you find yourself with a dead party of four, it means you didn’t retreat after the first death. And you didn’t retreat after the second death. And you didn’t retreat after the third death. Don't blame the designers for making a hard game, blame yourself for pushing a bad situation for way too long"
Scenario A) You hit the retreat button. You fail. Okay. You hit the retreat button again. You fail. That's fine. You hit it a third time. You fail again. The monsters go and kill/heart attack a character. You aren't healing because your trying to escape. At 2 heroes you can either hit the escape button again or (if you're lucky) heal each other. Since you can't out-heal the monsters it would be suicide to heal and wait for them to attack you. You click the button to run. You fail. You click it again. You fail. The monsters kill another character and put the other one on death's door. The remaining character is at 176 stress. You retreat. Remaining character stresses out and dies. TPK.
Scenario B)
Creator mocks you for being stupid and not running away. You kill one monster. Second character gets on death's door. You don't heal in time. Second character dies. Two remaining characters kill second monster. Big third monster puts one or both characters on death's door. Characters try to hit monster but or wildly out of position. Monster gets hurt at a rate of 12-24hp/round. After two rounds the monster is down to 40 some hp. Third character dies and fourth character has a heart attack. Now you deal 4 damage a round to said monster and it toys with you like a cat for three rounds before you stop "death's door"ing all the 20some damage attacks and die.
13) You realize that not only did you do nothing wrong, but you'd have been better off (as would your characters) if you'd just never played said round. You had made no longer-term (multi-mission) strategic errors. You lost your 8 best trinkets, which would take far more than 8 missions. It takes 10-12 missions to get a fresh meat character up to 5th level. You decide against the x3-x30 longer method of grinding and consider the above a "swingy" fluke like the beginning's play. You decide to pull the lever on the slot machine again.
14) two more missions and the above happens again. Two more missions it happens again. And two more and two more. You come to the realization that either the RNG is being manipulated at higher levels (further testing rules this out) or you realize that its simply a matter of time before another string of the above happens. When it does, it will end your run. The only question is if it will happen again before you "finish" the game.
15) You run the numbers. You'll get a string of 5 TPKs every 50 rounds in late game. It takes at least 10 rounds to get a character to a champion level run. By forgoing the above grinding tricks, you realize that late game is a slow, losing slot-machine gamble. You stop playing.
tl;dr Don't buy darkest dungeon. Like tic-tac toe, you're better off not playing.