Forget Sudoku. Kakuro: get your koat. Picross is the logic-based mind-meddler of champions. It's well established in Japan - having been invented by a woman flicking a skyscraper's lights on and off, believe it or not. Now the infection's spread to DS.
It works like PC timewaster Minesweeper with the randomness taken out. Starting out with a totally blank grid, you chisel out squares with your stylus, according to the numbers at the edges. So: seeing "3" and "7" at the top of a column means that, somewhere in that column, there's a line of three squares and a line of seven - in that order. The only question is: where?
Sudoku-heads used to just cross-referencing rows and columns had better upgrade their brain batteries now. Picross has no clues (unless you choose to autofill a single row and column at the start - wimp), so you really have to tease out the pattern, using knowledge of where squares definitely (and definitely cannot) lie. It's intoxicatingly logical and hard work. Imagine slowly illuminating a lightbulb with concentrated thought and you'll get a feel for how satisfying it is to watch the grid gradually fill up - blossom, really - as your beleaguered brain spots the rules and patterns. And - bonus - you've completed a nice picture of, say, a yawning hippo at the end of it all.
Picross DS is as technically perfect as you could wish for. Even the noise for chiseling away a block is just right. Scrolling the bigger grids around takes a bit of getting used to, but it reeks of care: the way the numbers scrunch up and follow you around to avoid getting pushed off the screen is just about the nicest thing we've ever seen.
You also have limitless user-designed puzzles from around the planet via Wi-Fi when the built-in 300 run out to look forward to. But that'll be more relevant for the US release, which has yet to be announced.