The core mechanic of the family is a variation of I cut and you choose. You can either draw a card or tile to add it to a group or take a group to make sets with. Your three best sets are worth happy, positive points. All the rest give you negative, sad face points.
I got Coloretto when it first came out, as you might guess from all the gray in my beard and the fact that I sometimes have to use a cane. And my initial experiences were terrible. I played with a group that focused on spite. The goal wasn't to get the most points but to bring the pain to everyone else.
After that, I did play games where people focused more on points than pain but Coloretto still didn't have that sing for me. Which was a real shame since it was and still is one of the most colorblind friendly color-based games ever.
When Zooloretto came out, it added a theme, slightly more complicated choices and an extra kind of action, the coin actions. It's still easily the lightest of the Schacht board games that won't be leaving my collection but those changes added charm and diversity to the game and those things made a huge difference.
As far as I know, Zooloretto has never been out of print and I've seen it in stores like Target aimed at the mainstream audience. I know it has been the real source of expansions and spinoffs and that my life would be better if I played Aquaretto. It is a game that has had success with both the broader audience and the serious gamer audience.
Zooloretto isn't my favorite Schacht game. (Hi, Web of Power family) However, I think it is the one that will go the farthest in the world.