Could be great, but isn't.
In theory, it's an excellent toy. Most of my cats loved it. But, a major flaw with this design renders it useless as a toy, only being any use as a scratch pad. Within a few days of use, the scratch pad creased in the middle, so the balls could no longer run the length of the box under the pad. This could be easily fixed by adding another pillar of scratch pad under the middle of the pad, as is used to support it under the corners. I would then give it 5 stars, but right now I am disappointed.