Nintendo, as ever, loves to mix up franchise's that have perhaps grown stale. Setting aside the success that the Paper Mario series has found, Nintendo took aim at the RPG series of Mario titles and ultimately settled down on the idea of Mario & Luigi: Dream Team.
Continuing where Mario & Luigi: Bowser's Inside Story left off, Dream Team has the duo taking off to Pi'illo Island for a vacation with Princess Peach. Of course, as soon as they arrive things go awry and the Mario brothers have to work towards discovering the mysteries of the island, before conquering the evil that lies in wait.
Like any normal RPG, Dream Team takes place in two distinct realms. There's the top-town world where Mario explores from level to level, dodging enemies and interacting with NPCs. Then there's the RPG realm where both Mario and Luigi fight enemies turn by turn.
It wouldn't be a Nintendo and Mario game without a bit of gimmick to it, however. As such, throughout the game the player is able to put Luigi to sleep on magic pillows. While Luigi sleeps, he's able to perform extraordinary things which both help in battle and open new areas in the overworld.
Dream Team also adds a different sort of battle where Luigi grows to gigantic proportions to fight opposing giant enemies. These become a type of rhythm mini-games, though of epic proportions.