Anyone else bought this? It's really quite good. And although I've never played Sudoku before, I completed my first puzzle in 15 mins 36 secs which gave me a "Train Speed" rating!
The mental arithmetic throws simple problems at you and you have to write the answer on the touch screen as fast as possible. It times how long you take to complete the task and you get a 5 sec penalty for any you get wrong. The basic level is 20 problems but the next is 100!
And the colour game is confusing - There are four colours as words and you have to shout out the colour you see. But if the word "Red" is shown in black, you have to say "black". It caught me out a few times

There's also a reading game where you have to read a passage from a book and a memory game where you see some numbers for about 2 seconds. You have to remember where they were and touch the empty boxes on the touchscreen in the same place you saw them on the normal screen - but in ascending order.
More types of puzzle are opened up as you progress each day.
Oh, and you hold the DS sideways with the touchscreen on the right...