Stolen from GameFaqs:
New Super Mario Bros Features:
-8 worlds with a theme to each of them:
1-Plains
2-Desert
3-Tropical Island
4-Forest
5-Ice
6-Mountains
7-Sky
8-Bowser’s Lair
Certain switches are located in some levels (World 2, you’ll turn the sandy ground into a mountainous dunes with the press of a switch, World 4, you’ll cross a deadly swamp by riding on the back of a dinosaur (Dori), and you’ll battle across icy slopes as snow falls from trees and threatens to send Mario sprawling in World 5)
-Around 80 levels
-The Koopalings are NOT in this game, it was rumored they were, but it’s confirmed they aren’t in this game.
-Bowser Jr. (He will be the miniboss of mid-way castles like Boom Boom in Super Mario Bros. 3)
-The world maps are like Super Mario Bros. 3
-Wall kicks and other moves are in from SM64DS (Triple jump, double jump)
-Hammer Bros. Are in the world maps again
-You can hold one item (Like Super Mario World)
-Optional Routes through levels reveal multiple paths on the world map, where you can use your Star Coins (Three in each level) to access extra areas and mushroom houses where toad provides extra lives or power-ups.
-Mario and Luigi control identically, which means that they have the same abilities, and Luigi CAN'T jump higher than Mario and Mario can’t run faster then Luigi.
-Yoshi is not in the adventure mode, but is playable in minigame mode. (Screenshot:
http://onnintendo.com/Posts/2006_04/25/2/00001.jpg)
-5 Red Coins are hidden in every level.
-Save after every world, and you can most likely save after each Mini Castle (May be other options like a "Suspention Save" where you save during a level or so, and continue right were you saved, like Super Princess Peach)
-No flying powers
-You can play through all the worlds in one play-through and it is possible to revisit worlds.
-One stage features you on top of a 50-foot long wiggler
Multiplayer Features:
-Single Card Play
-Competitive mode over wireless LAN (no Wi-Fi play) for 2 players, where Mario and Luigi compete for the most Stars throughout special levels including: Plains, Caves, Castles, Ice, and Pipe Mazes, you can also use power-ups to get the stars from your opponent, like: Stomping your opponent, stun him with fireball, plow with blue koopa shell, and there are also enemies in your way throughout the levels, and if you run into them, you will lose a star.
-Minigames, some new and some from Super Mario 64 DS, are here in four categories:
Action
Puzzle
Card
Variety
New Minigames include: “Danger, Bob-omb! Danger!” (move a Bob-omb to avoid fireballs);
“Whack-a-Monty” (smack Monty Moles as they emerge from the ground); and “Balloon Racing” (blow into the microphone to rush to the finish line) Some of the returning games form Super Mario 64 DS include: “Wanted!”, “Picture Poker”, “Hide and Boo Seek”, and others. Which all feature multiplayer modes, with single card support and 5 types of verses modes, like one designed specifically for one-on-one challenges (featuring games like “Bom-omb Trampoline” where you bounce a Bom-omb back and forth, and “Jumping Sudden Death” where you must tap your bro to keep him from falling on spikes).
Enemies:
-Pirahna plants
-Goomba
-Koopa Troopa
-Koopa Paratroopa
-Cheep-Cheep
-Hammer Bros.
-Blooper
-Bullet Bill
-Banzai Bill
-Dry Bones
-Lakitu
-Spiney
-Buzzy Beetle
-Thwomp
-Whomp
-Boo
-Spiders
-Boxing Boo
-Sharks
-Eels
-Giant Boo (May be boss)
Power-ups/items:
-Mushroom
-SUPER Mushroom (Makes Mario HUGE and allows him to destroy anything on the screen, rewarded with 1-ups for how much you destroy)
-1-Up Mushroom
-Starman
-Koopa Shell
-Blue Mushroom (Allows Mario to shrink and explore new areas and walk on water when running at full speed, but cannot defeat any enemies)
-Fire Flower
-Blue Shell (Allows you to stay stationary in water, and indestuctable out of water)
-10 coin block
-P-Block
Bosses:
Bowser Jr. (Miniboss of half castles like Boom Boom of Super Mario Bros. 3)
A Giant Goomba (Most likely King Goomba)
A Zombified sandworm
An enormous flying Piranha Plant
Bowser (First battle is Classic style)
Videos:
http://www.youtube.com/watch?v=3f1OHbt4JL4 (Shows Mario fighting a mini boss and the world map)
http://www.gametrailers.com/gamepage.php?id=836 (“It’s Mario super sized!” is a video that shows the intro and it shows the first level)