Brain Age's sudoku is decent and has a good interface, the puzzles themselves are good too. The complaints: it only has about 100 puzzles, so a hardcore sudoku solver will solve those in less than a week. It also lacks features and customization and there is only handwriting option to enter numbers. You also have to hold your DS as a book (though some might say this is a bonus).
Platinum Sudoku on the other hand has more puzzles (its possible to unlock over 20 million puzzles according to Ubisoft), unlockables, bonus challenges, visual tutorials, themes (you can customize and unlock fonts, grids, backgrounds, music), multiple input modes (handwriting and tapping), helpful options (highlight current row and column, mark easiest cell to solve, show possible numbers in cells), solver mode (enter your own grid and get a solution), option for creating your own puzzles, newspaper mode (disables all help). If you are a sudoku fan and done with Brain Age's sudoku, you might wanna try out this.
From japanese only sudoku games I would also suggest Sudoku DS : Nikori no Sudoku Ketteiban. I play it because of the simple and clean interface and one feature Platinum Sudoku doesn't have - highlighting chosen numbers on grid.