The world is full of interesting, challenging and useful mental problems—why devote your precious time to solving fake ones [like brain games]?

Why not use that time instead to learn Chinese, physics, computer programming, history, economics, calculus or millions of other engaging skills. Many of these have similar cognitive stresses that the brain games supposedly induce, plus the problem of transfer goes away since these subjects are actually useful…

Why pick a brain game when you can train your mind to do something useful and interesting instead?