One of my favorite genres is horror, which is notoriously difficult to create in TTRPGs, especially more combat-heavy TTRPGs like DnD. Horror relies on mood, atmosphere, and a certain feeling of being trapped and helpless -- at least for a while. When players can try to seduce just about everything and suddenly stop and make "Yo Mama" jokes, it can be hard to keep the atmosphere.
However, Six Faces of Death does an EXCELLENT job of creating and maintaining that atmosphere. It's a complicated adventure, but essentially Cube 1717 hurtles through the void to Acheron, becoming horribly warped in the process. It is found by/finds a quadrone, who merges with it, creating this rapidly replicating pixelating curse, which causes even more issues. Just when Cube 1717 looks like it's going to run out of steam, the skull lord Vargo finds it and manages to merge with it, gaining great power and greater ambitions. Unless someone (like your party) stops Vargo, it's going to keep pixelating the entire Material Plane.
The actual content requires a great deal of exploration, combat, and dungeon delving. The party is expected to explore the Changing Island, learning more information about the pixelating curse and what really is happening. After that, they find themselves in/going into Cube 1717, which is a series of dungeonlike rooms. Monsters, madness, curses, and conditions exist aplenty, and it might just be impossible for a group too hellbent on being murder hobos to make it all the way to the bottom. And, even if they do, they'll have to somehow overcome Vargo, who isn't going without some kind of fight.
As stated, this is a complicated adventure. You have an extensive cast of characters, a lot of enemies, even more motivations, and a thousand different ways the whole thing can play out. You are gifted with some pretty amazing maps, but it takes quite a bit of work for the DM to set this one up. It's not one of those adventures you can skim five minutes before a session and then make it work. I had to make notecards, maps, minis, and a ton of bullet points.
All that said, it is a great adventure, especially for parties that like a bit more combat. Yes, there are opportunities for roleplaying, but you've got to be active in this adventure. Sitting around too long can get you ambushed, flattened by a falling body, or worse. I upped the ante by adding in timers every once in a while, which really got the group moving. However, I really did have fun with it, and I absolutely loved how much it relied on Mordenkainen's Tome of Foes. SUCH great use of monsters!
One thing for people to be conscious of is the fact that it uses quite a few madness mechanics, not only with NPCs/enemies but also as effects that can happen to PCs. Madness mechanics can be insensitive or downright offensive for some people, so it's good to open up a dialogue about that. Similarly, the sheer amount of control and death in this adventure also necessitates taking breaks and talking through things. It can be a bit much.
Nevertheless, I really enjoyed this adventure and am glad I picked it up. It's also totally free, and the complexity, high quality, and INCREDIBLE maps make it more than worth it. Totally something you should grab.