I've played both Iji and the Chzo Mythos. My avatar is from a game of the developer of Iji.
When I first heard of how Iji was a game against violence I was intrigued since that is something that turns me off from plenty of games. I played it through two times: first time where I used violence the whole way and the second time where I played pacifist.
Playing pacifist gave me the disturbing realization that the average violence-hungry stereotypical gamer I encountered online had a lot more in common with me than I would have liked. Because the game more or less played the same without the core component of the combat present, and the bad guys of the plot mechanically reacted similarly. (with violence they go: "You want us to leave? After you have mowed down untold numbers of our troops!?"; without they go: "You honestly think we'd leave just because you ask politely?"). At which point pacifism only felt encouraged from moral principle, and finding out I did not find that sufficient was a bit disturbing. Although I understand the developer has made a patch that makes pacifist play more satisfying since then.
Onto the Chzo mythos: I only liked the first game in the series, 5 days a stranger. That game has you playing as dashing cat burglar Trilby, trapped in a mansion, solving a ghost mystery. The thing I liked about the game was that I wasn't frightened by it, it felt like a mystery game with some scary bits, and it was relatively down to earth; while I do not believe in the supernatural the occult stuff in the game was on a level where I could find myself believing that it *could* be true. Since you furthermore solved puzzles by using things you could find around a normal house it also felt within the realm of my own capabilities and therefore more relatable.
The sequel 7 days a sceptic made the mistake of thinking that it was the ghost that was the interesting bit, and made an Alien rip-off about a killer ghost killing a space crew. That switched the genre from mystery to horror slasher, which since I am not a fan of violence and horror cannot say I approved of. What's more, since I knew how the ghost operated it turned into a game of watching people behave in an irrational way, and since it was set on a spaceship the puzzles were not really relatable to real life.
Trilby's Notes is a game that is probably what the first sequel should have been since it stars the charismatic lead from the first game and he is once again solving a mystery, with a better in-game reason for why he cannot escape his predicament. Were it not for one choice made I probably would have enjoyed this title a lot more than I did, and that is that it was so bleak. After the first game the survivors made their way out relatively unscathed in a way that left me feeling uplifted for the future; this game starts by revealing that all the survivors in essence had had PTSD or other problems from their experiences. Which is a natural way for their characters to go, but it put me in a bad mood that colored my experience with the game badly, and made me less forgiving of aspects that had I been in a better I would just have rolled with. Which is a shame, since Trilby's Notes is frequently cited as the best in the mythos.
6 days a sacrifice is the worst in the series. The plot assumes the player is familiar with the mythos, while having a protagonist that is basically clueless. And the puzzles were uninspired and contextual as heck, and I don't think I liked any character in the game. It also felt like it was more interested in putting a bow on itself rather than telling an interesting story, kinda like Metal Gear Solid 4 if reviews are anything to go by.
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If I had to pick a series I'd probably go with Iji. Both series are bleak, but Iji at least has interesting repeatable mechanics(gunplay and hacking) whereas the puzzles in the Chzo Mythos felt secondary to the story, and If I already did not like the story it makes sense that I consider Iji stronger.
