A flawless game, but much too short.
The story is easy to follow, and makes....enough sense. The only problem is that at the end of the game you'll say to yourself "Wait....how did this all start again?" It's not a real complicated story, though.
As you walk around the "dungeons" in the game, you'll solve puzzles that are pretty easy. For 1/10 of the puzzle, you'll be thinking to yourself, "Okay, I have to do x to y", but then 15 seconds later you'll realize that you're doing it wrong and then you'll do it the right way, and you'll realize how easy it was.
In the puzzles, you use your abilities that you unlocked in the game to solve them, so for instance you could see this huge gap, you'll say "Yeah, and I'm supposed to JUMP across that?" Then you'll learn the Spin ability and then you'll just tornado across the gap.
The combat is perfect. You don't have a lot of moves to do, and unlike the console RPG's, you'll be using A LOT of items, so don't be afraid to spend all your money on them. When you first use an item, you'll look like a foolish moron as you try to do damage with them. After a while, you'll get the hang of it and take some names, but after a half an hour is where you really kick some butt.
Some examples of the items are the fire flower, where you press Mario's button repeatedly, then you'll press Luigi's button repeatedly, and switch back and force until the fire flower's out of juice. Another one is some crazy egg thing where Mario and Luigi will do cool backflips to smack them at the enemy.
Timing is everything in combat. When enemies attack, you have to know how they're going to hit you and when to hit them and with who. Same as I've been describing. First time you see an enemy, you'll stink, after awhile YES BLAH BLAH BLAH WE GET IT!
The sound and graphics are charming and cute, and they make the game a lot easier and more enjoyable. Nothing to rant about.
What also makes this game such a piece of art is how hilarious it is! Luigi's always the clumsy dope who is always accidentally making his baby form cry and then he cheers him up by doing ridiculous things, and Mario's always smooth and cool about everything. It gets me everytime.
The only thing that breaks this game is how short it is! It'll take you from 16-24 hours to beat it, and there really isn't any fun left when you go back and play it again, but this game is still a must-buy.
There is also no use of the stylus or the touch screen, but it really doesn't matter.
There are almost no flaws in this game, except it's length (comparing it to other RPG's). I recommend it to anybody who owns a DS.