Let's a go! The E3 demo for Mario & Luigi Dream Team features three scenarios: exploring the real world, the dream world and a boss battle example.

I got a chance to try out the real world scenario, which features some lush overworld plains, not unlike the opening areas seen in previous titles. The biggest and most obvious addition to the franchise is the graphical overhaul, presenting the world using colorful and simple 3D models with cartoonish textures. The characters are 2D sprites, but they lack the cartoon outlines and pixel look from past titles in favor of a new painted style. The animation is as fluid as ever, with plenty of squash and stretch as the Bros. bounce around the screen stomping enemies.

As can be expected, the A and B buttons are assigned to Mario and Luigi respectively, and they jump independently from one another to traverse the landscape. Plenty of staple elements to the Mario & Luigi series are present right from the get go, and pressing the R button will cycle the jump command to hammers and specialized jump techniques. I noticed hidden "x" spots in the ground where Luigi could hammer Mario underground and pop out to reveal buried beans. Various seesaw platforms that required hammering would allow you to spring yourself to new locations or rearrange the height of corresponding platforms to create staircases; there seems to be plenty of puzzling platforming action to be had in this title.

One new jump technique was a special drill move that sends Mario and Luigi hurtling forward and smashing through rocks, which was used creatively in one valley area where the Bros. fly into a suspended, rotating cannon and then fire themselves out in a different direction to smash boulders blocking their path forward. 

Overall the game looks very promising, and features the same style of humor and charm present in each of previous titles. I'll go back in for another crack at the game over the course of the day and I'll be back to update later on when I've had a chance to play the other two demos available here at E3.

EDIT: After getting some more hands-on time with the game, I'm able to shed some more light on the other demos. The second playable scenario features Luigi's dream world, the inhabitants of which appear to revere Luigi as a kind of omnipotent, "Luiginary" being. In this world which is presented as a 2D sidescroller, when an enemy attacks the Bros, only Mario will intially be present to do battle. In these solo battles, Mario is given a little more freedm of movement to dodge and counter enemy attacks, and he can run up and down within a small space on his side of the battle screen. A new Luiginary battle option is available here, which lets Mario summon a massive group of Luigi clones called Luiginoids to assist him in battle. These are the attacks seen in the promo videos. The first one, Luiginary Stack, has groups of Luigis charging forward in a crowd and hopping onto other groups, eventually piling up into a tower of green Luigi stompage and dropping onto the opponent. The other, Luiginary Ball, has Mario rolling an increasinly large ball over a long winding trail of Luiginoids to bowl into the enemy, squishing it in their path. It was the boss battle demo that also featured these battle tactics, with Mario fighting Bowser by himself with the help of the Luiginoids.

At certain points throughout this dream world, Luigi can interact with the scenery to create various structures for Mario to climb on, such as a leafy mustache that could stretch by manipulating the sleepy Luigi's mustache in the real world, making it latch onto Mario and slingshot him to new heights. Another scenario showed Mario hopping onto a giant stack of Luiginoids and smashing through cliffs and floors while trampling enemies. The whole game oozes with personality and quirky dialogue, and it's bound to be a hit for players who liked the previous games.