Honestly, just read the other negative reviews. The crimson curse mechanic essentially removes Heroes from your Roster while they have it, which happens extremely quickly. Enemies that have a 30% chance to inflict it commonly spawn in random encounters (Syncopants) in packs of two, with a speed rating of 10 (which is way more than any non-endgame hero will have), and if you're unlucky, both will inflict the crimson curse on different heroes in your party in the first two actions of combat before you have any chance at counterplay. Once they have the crimson curse, they are debuffed for around 50% of your entire save state or game run, and risk infecting other heroes if they even share the same building in a stress relieving activity (you know, the ones you regularly use to counteract the main game mechanic of stress?).
Apart from that, Red Hook introduced a new kind of ridiculously strong random boss (like the Shrieker or the Collector), the Fanatic. Imagine a Hag on crack. He also has a couldron, only it's a stake, and he removes heroes from your roster. Sounds not too bad, right? Well, where the Hag has two actions per turn, he has three. Where the Hag has a total of 4 abilities, he has 5. Where the Hag has anywhere between 0-27 Dodge and no PROT, the Fanatic has 3-25 Dodge, and 15 PROT - which he often buffs through abilities that still deal large damage to up to 65 PROT. Remember, during this, he still has 3 actions and you only have 3 heroes. And the best part? You can't even prepare for him! The Hag you know you'll face because you select the mission. You know you'll face the Fanatic because the game tells you in the loading screen (so after you've assembled your party) - and at that point you can essentially abandon the quest. You got a marking party? Too bad, the mark is gone after one round because he has three actions. Speed-based party? One of this attacks inflicts a -3 speed debuff. He takes your Healer to the stake first? You're fucked. He takes your back-rank damage dealer? Also fucked, as characters are released from the stake in rank 1. Apart from that he has a high-percentage stun which also deals high damage, inflicts stress, and moves the target back (effectively leaving you with 2 heroes for the turn). He is no fun to play against unfortunately - he is not challenging, just plain unfair. Against any other boss you can determine their weaknesses and create a party accordingly, you can prepare and plan, and if you're unlucky, you might still get fucked - that's Darkest Dungeon. But with him, you can't prepare, you can't plan ahead, he is a random encounter and he will fuck your party. A randomly appearing boss that is worlds stronger than an actual boss in the game (yes you can avoid him by not using crimson cursed heroes - but at some point in the game so many heroes have the curse that this is impossible to avoid).
People will say git gud, or that I'm obviously not the target audience for this game, or any kind of bs "look at me I'm so tough" excuse because they never had anything anyone was ever proud of them for - but honestly, if I'm voluntarily disabling content I PAID FOR because it is so unfun, that's a line to me. Completely unfortunate, the enemy design is great as always and the music is oh-so-good. The theme of the DLC is great and fits in perfectly. But gameplaywise, this DLC is bad and not fun. I love the base game, but don't buy this.