Sudoku: Grid Master: one word: disappointing
For one, the interface is ...redundant(?).. there's really no need for the top screen at all for instance, its just a double of the input screen. You just use the stylus to select the box you want to put the number in, then tap the number, simplle (there's also apparently a handwriting mode, but personally I haven't tried that, as the novelty of sudoku just doesn't call for it). If you press one of the triggers it highlights the row, column, and 'box' that you're in, but honestly I dont see how that really 'helps' you solve anything (or is that just me).
Music..um..yeah. I tend to like game soundtracks, and while Sudoku: Gridmaster's music is (I guess) supposed to be soothing, it drives me up the wall, and unless I missed something, options do NOT let you turn it off, you have to resort to a big wooping 3 choices of music, or use the volume control on the DS itself to mute it.
Multiplay: none, granted, Sudoku isn't a multiplayer game to begin with, but even Brain Age's enclosed nugget of joy compared you to other players, no such luck on this one.
All in all, if you're looking for an assortment of sudoku puzzles (and you have a DS), then this is ok, but quite frankly I like the collection (and interface) of the puzzles in Brain Age much better.