I'm not sure where the great "artistic" appeal comes from, but the Holga certainly produces a distinctive "look" that one can learn to use to an advatage. Part of this appeal has something to do with the natural vignetting produced by the lens. Apart from the outer edges of the frame, they take remarkably good pictures.
I bought a couple and fooled around with them a bit. They are fun yet can be a royal PITA with light leaks and all the tape necessary to stop them. They do demonstrate that its not necessary to have a fortune in fancy gear to take good pictures. Not a bad way to learn basic photography skills.