It's an interesting idea, that turns great with another person, but it's an idea that only remains fun for so long.
Brain Age revolves around the idea that when people stop using their brain that their brain gets old and inefficient. Luckily, Brain Age contains a number of activities to keep your brain young and healthy. The game will show you how much you have progressed over time with graphs. You can also take a test to see how old your brain is, with 20 being the ideal age. The game also comes with many handfuls of sudoku puzzles, which also are supposed to keep your brain in shape.
You play the game with the touch screen and microphone alone in the activities. You also play the game by holding the DS sideways, which will seem strange at first, but actually works out fairly well. The main tasks you have include math calculations and reading abilitiy testers. Eventually, you unlock plenty of other modes. These modes can pretty addicting, and you'll have the incentive to want to beat your own score, or better yet, the score or someone else who has their own progress being saved on the copy of the game.
The fact that the game sorely uses the touch screen and microphone can be an advantage and a disadvantage. The controls with the touch screen feel intuitive, but sometimes the littlest dot could make the game think your 2 is a 7 and since you get penalized for making mistakes, this can be quite frustrating. The microphone also works pretty well, but it could also mistake one thing for another, but most of the time it works pretty well. It should be noted that the game is meant for native speakers, so if you have an accent of some kind, you might run into problems.
The game isn't thriving with polygons or the biggest graphical effects, but that really doesn't matter, because this is more of a tool than it is a game. You shouldn't be expecting too much from the audio department, because you really wouldn't need to hear music or any sound effects for that matter. You shouldn't worry about the presentation too much, because it really isn't needed, but it would have been nice.
The appeal of the main game doesn't last too long if you don't have another person to compare progress with, but if you do have someone that could be potentially interested in this game, it might be worth looking into, especially since it's at a budget price. There is also a bunch of sudoku puzzles to keep you interested. The game also features multiplayer, but this is just a basic test to see who can math problems the quickest. The game could have lasted much longer with the ability to transfer graphs with your friends, or possibly, around the world with online play.
Brain Age is an interesting application and it might be worth looking into, whether because of the basic puzzles it features or whether you're just looking for something new or interesting at a budget price. Puzzle fans are bound to like it, but they should question whether or not if it's worth buying if they won't be playing it for anytime too long.