I always thought of the series as something special in the context of shmups, because it was developed by Eighting, former staff of proficient studios Raizing and Compile, and the main focus is similar to shmups (dodging stuff)!
It's inspired by three video games released in 1997/98, which were in turn based on Japanese game show ウッチャンナンチャンの炎のチャレンジャーこれができたら100万円!! (lit. "Ucchan Nanchan's Challengers of Fire: 1,000,000 Yen If You Can Do This!!"), where you have to guide a metal rod through mazes without touching the walls. An idea you probably have already seen in some simplified form in the context of toys, children's parlor games, or carnival and is much older. The show ran between 1995 and 2000.
The Irritating Maze (Neo Geo, '97)
The other two preceding games:
Spoiler
Spoiler
Personally, Kuru Kuru Kururin is one of my absolute favorites on the GBA and I've 100%ed it a few times already. I began Kururin Paradise (also GBA) a few years ago, but didn't persevere until the end for one reason or another, which is a shame that I definitely intend to remedy at some point. I have no experience with Kururin Squash! on the GC, but I have heared that it's allegedly overshadowed by its two predecessors.
I'll definitely follow along the AGDQ run of the first game, as I think it'll be one of my favorite runs besides Gus' Futari performance
What's your opinion on the series?
(click on image for Hardcoregaming 101 articles about the Kururin games)