I feel like I'm just being delusional and old but I remember being super into 2kki around 2017-2018 because it still elicited a very specific feeling, one which I don't get much anymore when playing the game now. I'm not sure if it's the new online nature that changed it for me but I feel like it started before then. I'm saying this because I got the feeling again when watching this video:
https://www.youtube.com/watch?v=ALjswC_iej0It's like a specific dark atmosphere is present… the color black is used extensively to create contrast and add depth to objects in a certain way, this is a pretty crucial component of 20's artstyle but it's present in mostly all the early authors' worlds. Objects are more likely to do unexpected things, there is a general feeling that you should expect the unexpected and that even a cute looking world could change to something weird or unnerving easily. There is more focus on collecting effects because the game is smaller, interactivity in each world is generally higher.
The original Yume Nikki always had a sense of depression overlaying the whole game, I think what made 2kki special is that it didn't and you genuinely couldn't expect what would come next. There seems to be an inclination for newer worlds to stick to a singular tone only as to avoid CUTE THING BECOMES EDGY cringe, yet older worlds pulled it off very well - take Japan Town for example, where the cheerful main street becomes the creepy hotel, or in Flying Fish World where a calm open space leads to a strange laughing woman. Even the best modern authors like Qxy generally don't do this and I wish they would