For RTS fans with a DS, 1701 AD is a must have. Not a kid's game.
Kids might not appreciate this game as much, as the strategy is fairly deep for a DS title and the AI is quite tough. But for someone a bit older, who wants a good strategy game to play on the go, 1701 AD can't be beat. Being able to save at any point in the game and to start where you left off later is particularly handy. I especially enjoy the Sandbox ("Continuous") Mode, where you can tailor a game to your own specifications. Plus, the game has a multiplayer feature.
My quibbles are minor - I wish the AI could be set where it wasn't always so effective and strong, although one can shut off all the independent AI players in Continuous Mode and just play against the pirates. It would have been nice to be able to save more than one sandbox game at once, or to be able to rotate the map. But give that this game is playable on a DS (!) it's a shock that the Sunflowers team managed to get as many features on as they did. This game really pushes the envelope on what a DS can do.
There's a reason why this game was a smash hit in Germany. I highly recommend it.