Graphics: 3/5 Not much to speak of. They're just really average, and well under the 150 MB graphical limit.
Sound: 3/5 A simple tune in the background is basically all you hear, with the occasional "Good job!" thrown in there. Also average.
Control: 4/5 The stress games really make for some weird controls - but that's exactly the point. My only REAL problem with the controls is that the analog stick skips too far sometimes when you move it once. Besides that, everything is pretty simple and uncomplicated.
Fun: 3.75/5 Brain Challenge is probably not worth the $10. Definitely five, for sure, but $10 is pushing it. The game isn't bad, but the mini games aren't all interesting, and there aren't many features. The multi player is decent fun, if you can even connect to a room. I recommend getting it only if you haven't yet tried Brain Age or a game similar to this.