It's been so long that recalling all the reasons KidPix made me happy would be impossible. But I can remember spending hours using that app, doodling, making little movies, and just enjoying everything about it. Little touches like the "Oh No!" sound effect made the app so much fun to use.

The app was bought (along with the rest of Broderbund's IP) and resurrected a couple years ago:

http://www.mackiev.com/kid_pix.html

Not sure if it lives up to the original.