[Update]: Darkest Dungeon 2 is heading into Early Access on October 26, 2021
While not exactly the most Christmassy game given that it's all about suffering, madness and death, Darkest Dungeon is still a pretty darn good game to spend the holiday season with. As such, I am more than happy to say that the Epic Games Store is currently giving it away for free!
Naturally, the giveaway won't last long, so make sure to pick up your Christmas present sooner rather than later. Once you have it unlocked on your account you'll be able to play it whenever you want and for however long you want, so a little bit of haste right now is well worth it.
Before you begin your adventures, it is also worth mentioning that Darkest Dungeon is a remarkably challenging game. If you're going into it blind and don't consult any walkthroughs, there's a high chance you'll lose a whole bunch of your best characters before even reaching the endgame. I'm not saying this to discourage you, however, but rather to help you steel yourself for what is to come.
Darkest Dungeon is a great game, and part of what makes it great is the risk involved, so just accept that sometimes bad things will happen and roll with the punches. It'll be worth it in the end!
Have fun, and I'll leave you with one of the trailers:
