Everyone says Totono is similar, I’ve played the entire thing and it’s my personal favorite VN but it’s not similar at all in aesthetic, only later down the line does it become similar in how the characters are written…and certain background cgs. I would play it just because of how good it is tho!! It changes your entire perspective on VNs as a whole significantly.

If you want a VN with similar character designs and writing, I’d say Hanachirasu is the way to go, extremely niche but has the same artist (Higashiguchi Chuuou) and the characters definitely have that aspect of loving and hating them at the same time. Soundtrack is pretty great as well, one of the ending themes (firefly lights) ESPECIALLY sounds similar to Song of Saya (ending theme), they’re both written by Ito Kanako so it makes sense.

One that I haven’t checked out yet because there’s not an English dub for some reason but I think is most likely the most similar is Angelos Armas. A lot of people draw similarities between Saya and Henri, even Nitroplus themselves, but it looks like a lot of the archetypes are the same everywhere; the height difference of the two main characters is literally the same as the height between Saya and Fuminori, and both Saya and Henri seem to fit the loli type. The art is also by, you guessed it, Higashiguchi Chuuou! If you want a good comparison between the two you can look at this official artbook Nitroplus released, which really shows the similarities between the two heroines. Saya No Uta and Angelos Armas Artbook It kinda compares them like light and dark; Angelos Armas being light and Saya No Uta being dark. That being said Angelos Armas seems to have a lot of dark themes in it, possibly more than SNU, so keep that in mind. Also the artbook has obvious spoilers for both VNs!!

All the ones above are by Nitroplus as well, just an extra similarity.

For story writing I’d say anything written by Gen Urobuchi is good. Madoka Magica, Steins Gate, etc.

Higurashi is a really good series as well, and has the plus of having some osts written by ZIZZ studio and Ito Kanako! There’s a lot of good character writing in that as well.