"Beef? I am lacking in beef. Fawful is beefless."

Mario and Luigi first shared the spotlight in the 1983 arcade game, Mario Bros., where they teamed up to clean sewers by stomping bad guys. Although we immediately fell in love with them, the silent twosome's lack of personality left us with more questions than answers. The mysteries continued well into the Super Mario Bros. games, with the plumbers exploring the Mushroom Kingdom to rescue a princess from the clutches of their arch nemesis, Bowser. Nintendo did an admirable job adding character to its quiet mascots, but we wanted more, something we still didn't receive with Super Mario 64, Super Mario Sunshine and even Luigi's Mansion.

Thankfully, Nintendo satisfied us with its critically acclaimed Mario & Luigi series. These portable role-playing games are the perfect compliment to the Paper Mario adventures on N64 and GameCube, and they also provide a much deeper look into the minds of the company's franchise heroes and villains, including Peach, Mario, Luigi and even Bowser. On top of that, each game features outstanding and at times humorous dialogue, as well as simple and addictive battles that are less about item management and more about having fun.

When Bowser goes down, the plumbers will need to fix the big oaf from the inside.

Mario & Luigi: Bowser's Inside Story continues this tradition, with a marvelous narrative and enjoyable combat. Except instead of swapping between the plumbers and their infant selves (as we did with the equally phenomenal Partners in Time), you wander through Bowser's body solving puzzles, fighting monsters and manipulating the giant brute to do your bidding. That alone would have earned high marks, but Nintendo didn't stop there. The game's designers let you switch between Mario, Luigi and Bowser on the fly, essentially providing you with two beautifully woven adventures. The result is a magnificent DS game that raises the bar not only for the series, but RPGs in general.

In this charming adventure, a strange disease called "the blorbs" rips through the Mushroom Kingdom, causing peaceful Toads to balloon up and roll uncontrollably. Peach and her council of advisors immediately summon Mario and Luigi, and you'll start laughing the second they arrive; in typical Luigi fashion, the clumsy brother loses a shoe, then falls asleep at the meeting.

As expected, Bowser charges into Peach's castle looking for trouble ("Did someone just page the king of awesome?"). Mario teaches him a lesson, then punts him into a forest. Upon waking, a strange figure tricks Bowser into eating a mushroom that gives him the power to inhale just about everything, most notably, Mario, Luigi, Peach and a bunch of Toads. That's when the shadowy mushroom peddler reveals his true identity. It's Fawful, the mad scientist from previous Mario & Luigi games, and he intends to take over the Mushroom Kingdom and pull Bowser's strings.

To thwart his evil schemes, Bowser stomps through the Mushroom Kingdom solving puzzles, defeating enemies and using his fire breath to burn trees, thus revealing hidden paths. But he can't do this alone, and that's where Mario and Luigi come into play. You seamlessly switch between the brothers (who are trapped inside Bowser's body) and Bowser, using the DS face buttons. Even better, Nintendo designed all of the characters to work in tandem. So, for example, if Bowser ingests a lot of water, his body floods and Mario/Luigi can swim to previously unreachable areas. Conversely, the brothers can give the big lug a power boost by smacking his nerves with hammers. In one instance, they repeatedly hit one to increase Bowser's arm strength, allowing him to pull a small island with a rope. You'll also encounter boss fights where Bowser will need to inhale a piece of his enemy so that Mario and Luigi can damage it.

At first, switching seemed a bit stressful, simply because the game's so enormous. Every time we left the brothers in some part of Bowser (the Chest Station, Nose Deck and Nerve Cluster, among other places), we feared that spending just ten minutes wandering around an island (Bowser's first stop is Plack Island, a place with humongous and cavity filled teeth) would negatively impact the plumbers' adventure, but that's not the case. Nintendo skillfully blended both segments, with players swapping characters every few minutes. Because of that, you'll never feel overwhelmed.

Bowser's body reminds us more of Metroid than one of those nasty operation shows.

As for the battles, they bear a striking resemblance to the ones from the prequels, in that they're easy to figure out while at the same time providing a hefty challenge later on. Whereas other RPGs force players to wade through menus, Bowser's Inside Story features a scrolling wheel over each character's head with icons representing various attacks and the all important Star Menu, where you can use power-ups to replenish hit points and what not. From there, it's all about the timing. When attacking a monster with Mario and Luigi's jump, for instance, you must wait until either brother leaps into the air, and then press the corresponding button in time to deliver the strike (press it again for double damage). With Bowser's flame breath (and Mario and Luigi's hammer attack), you wait until the last possible second (characters will wind up) before mashing the button. This carries over to special attacks, where you'll need faster reflexes to get the job done.

In addition, you'll also need to stay frosty on defense. As monsters attack, you can deflect their blows and possibly even damage them if you get the timing down. This proves critical in one of the early boss fights, where failing to properly defend Mario and Luigi results in the monster healing itself. Bottom line, this level of interaction makes fighting more enjoyable than your typical RPG, where everyone just stands around watching attacks.

Of course, battles are just one of the things you can do. Mario and Luigi will hunt for Attack Pieces (find ten to learn a new attack), while Bowser will scour the land searching for Blitties, these weird cat-like blocks, to give to one of the game's best characters, Broque Monsieur.

That leads us to the game's magnificent presentation. Everything about Bowser's Inside Story screams high quality, starting with the aforementioned dialogue. There's a lot of cool tongue-in-cheek stuff right from the beginning, where one of the Toad's says to Mario, "How's the jump holding up these days? Knees OK?" That's just one example of the funny lines you'll come across; we laughed at stuff like "Fawful is gorging on his plan of win! And still he as hunger!"

We also chuckled at Mario and Luigi's Italian gibberish, Broque's French dialogue and calling Bowser, Monsieur Turtle Bits. These are small things that combine to form the game's overall identity; wait until you meet the Emoglobins.

Visually, Bowser's Inside Story shines, with colorful and happy environments bursting with detail. With the Mushroom Kingdom, Bowser makes his way across sandy beaches, sky blue water and through forests, among other locales, while Mario and Luigi explore a sea of muscles, nerves and tissue; none of this stuff looks gross, by the way. Even the tiniest thing, like how one brother will walk over and pick up his unconscious partner during a battle, enhances things tenfold.

That also applies to the audio. We already touched on Mario and Luigi's unintelligible Italian, but there's also various sound effects and a remarkable soundtrack that changes as you go from inside Bowser to the outside world. Doesn't matter if it's the battles, graphics or music. Whoever made this game, did so with tremendous amounts of love.

That's what ultimately makes Mario & Luigi: Bowser's Inside Story so incredible. It's one of those rare games that received enough time and attention to make it sensational, a real treat for DS/DSi owners. At this point, we're not sure how Nintendo will top it, but we also said that about Partners in Time and Superstar Saga before that. In short, Nintendo releases this gem September 14th, and you'll adore it.