Well, I'm glad you asked!
{INSERT LONG NIKKI FRANCHISE HISTORY POST HERE}
...No, I have no freaking idea. I even looked it up a bit and still don't know how to explain or figure out this game series. I just know some girls in my circle who play them.
For what I understand of it, Nikki started as a general dressup game for girls (and creepy boys,) but it had some story and character visual novel elements to it too. As the games progressed, the adventure stuff got bigger and crazier. (Like, their trailers all seem to have no gameplay or even game engine, just
pictures of war and churches and dancing and fashion shows and violence and angst??) There's also social media hooks for sharing your designs with the Nikkiverse (and I assume all that deep lore fuels the drive for engaging in fanart/fanfic.) The series started out with typical cellphone 2D paperdoll graphics, but by the fourth game Shining Nikki, developer PaperGames had built a
sexy 3D engine, which has now allowed them to go anywhere with their future projects.
https://lovenikki.fandom.com/wiki/Category:Games
So, short answer to your question of "What was Nikki 1-4 like?", the answer is, not like this... or maybe just like this? Hard to say, since every time they show you a Nikki in a trailer, that may totally or may not at all be the game you can expect play.