Some of the games seem too easy for me.

That's on purpose! Dr. Kawashima, world-renowned neuroscientist and developer of the Thinkie brain games says "My research shows speed with accuracy is more effective than complexity. The games seem simple, but they are not. They are designed by neuroscientists who study what activities lead to more blood flow to the brain, and therefore work the brain more. Although it seems counterintuitive, simpler games are more effective for users of any age."