Sudoku, for those not in the know, is a number puzzle where players use the given clues to arrange numbers one through nine in each row, column, and every three by three grid in a nine by nine game board. No number can be duplicated in those locations, which means there's only one answer to each Sudoku puzzle. It's a simple concept with a gazillion different ways to play, and each puzzle's ranked in difficulty based on the clues given from the start.
Sudoku Gridmaster is obviously a product done by a completely different development studio than Brain Age. In fact, the game feels an awful lot like a contractual obligation between Nintendo and Hudson - Nintendo already had a Sudoku hit with the version in Brain Age, but instead of building off of that engine, the company instead went with a totally different product with a presentation that doesn't look or feel anything like Brain Age's sterile-but-very functional Sudoku mode.
Is there anything really "bad" about Sudoku Gridmaster? Nope. For 20 bucks you get more than four hundred puzzles that are timed, ranked, and can be saved at any point. You can compete in four different challenges if you earn enough credits solving the Sudoku puzzles. But that's really everything that can be said about the product. Gridmaster has a sleeker environment with more attention paid to its visual presentation, though, honestly, since the game's all about a simple nine-by-nine grid with numbers to organize, Sudoku is not about the visual appeal.
Unlike the Sudoku mode in Brain Age, players can input numbers either by tapping on a keypad on the right hand side of the screen, or scribble the numbers in using handwriting recognition. This handwriting engine isn't handled nearly as well as Brain Age, so those who put a little loop in their twos or write their fives like a flat-top letter S will have to relearn their penmanship. And since you're writing the numbers in a data entry grid detached from the main Sudoku grid instead of scribbling the numbers directly into the specific square, it's not as intuitive to input numbers this way. It's also a little clumsier this way since you have to trigger "note mode" if you want to enter smaller, unofficial numbers into the square to keep track of possible entries.
On the upside, there are cool little features in place, like the ability to highlight all of one row, column and quadrant by tapping the L or R trigger. You can also cause all of one number to flash on-screen by double tapping the specific digit - a handy tool to spot possible goof-ups. On the downside, the cart only holds one user profile, and can only save one active puzzle to memory.