Great game, but if your child is too young...
I just want to write this review for people with children who don't know about games. Some people hear the name Mario and think it's great for their 4 yr old that just got a new DS. This Mario game isn't the simple run to the end of the level while jumping on enemies heads and collecting coins. This game has puzzles to solve that may be too much for children that are too young. And a lot of story that a younger child won't know to sit and read through. Older than 4, maybe 8 yrs is good, but it depends on the child, too.
Otherwise, it's a great game with a fun story. You need to combine Mario and Luigi's skills and help them to new areas as a team. You also can switch to Bowser to help get through certain obstacles too big for Mario and Luigi. It's also good to learn where you can save your game and do so as often as you can in case you make a mistake or you have to quit the game. It's a good adventure with great humor in it. It also falls a little into the RPG category of games. Mario and Luigi get experience and you can increase their stats so they can take on bigger enemies and gain new attacks.