If you want something classic and difficult, Tokimeki Memorial is as pure as it gets. You will have to micromanage everything to succeed, and a guide is recommended. You would have to use a fan translation for it right now, but it's getting an official English version this year.
A lot of dating sims have a focus on visual novel elements without much combat or anything else. Clannad is my personal favorite in this vein, and Steins;Gate is very good too.
If you want something with nsfw content, a lot of the older Japanese made VNs have something that you'd have to download a patch to see. Nekopara and The Fruit of Grisaia are two examples of this, but watch out for uncomfortable topics and themes in these, especially in Fruit of Grisaia.