A worthwhile challenge for puzzle fans but the eStore offers better games in this vein now.
The game is played pretty much entirely w/ the stylus on the DSi's touchscreen. (You can scroll the screen using the d-pad but that can also be done via the touch screen.) Your job is to manipulate the world in such a way that thoughtless wind-up Mario toys reach can reach their goal.
It is all relatively straight-forward and the concept is solid. Nintendo does a good job here of using relatively few puzzle elements to create a varied challenges out of a simple framework. Most gamers will wind up beating at least some stages by an arduous trial-and-error process (made slightly annoying by the fact that you have limited lives, despite the fact that running out of lives has absolutely zero negative effect). Unfortunately, it feels like many of the stages are beatable by just simply trying random things until something works. On my own play-through, I managed to beat a few levels accidentally. Despite a few levels that don't quite work, Minis March Again offers a good and nicely scaling amount of challenge.
There is also a decent amount of gameplay here. The game appears short at first but after the initial set of levels are beat, a game-plus mode is opened and that offers an equal number of additional levels. These really aren't much more challenging but the gameplay slightly differs in that on the main game the wind-up Marios are manually started by the player and in game-plus the Marios startup automatically. Additionally, completists and challenge-seekers can open up yet more levels by going for high scores to unlock even more levels. While it only takes a few hours to play through the main game, there is much, much more than that if you wish to delve in further.
Mario Vs. Donkey Kong: Minis March Again is a great little bit of fun. It is certainly one of the better DSiWare releases but that is not exactly the highest praise. Now that Nintendo has raised the bar w/ their eStore service for 3DS, if you have the newer handheld, you will get better value buying Pushmo or the upcoming Crashmo from that service instead. Still, those who like puzzles will surely find this to be a worthwhile purchase.