IMO, it's easier to decide for yourself. So, here are most of the features included in Brawl:
39 playable characters of varrying fighting styles. Another 29 major characters appear in the form of Assist Trophies, where they will come out and fight for you.
Subspace Emissary. A 10 hour single-player adventure mode featuring all characters in the game interacting in an intertwined story. 2 player co-op in this mode. 5 difficulty levels. Includes an RPG like stat increase system where you attach stickers to your character's stat board to boost their abilities.
Over 300 musical scores composed by the best song writers in video game history (Nobuo Uematsu, Motoi Sakuraba, Akihiro Honda, etc.), and the ability to pick what songs play and how often in each stage. These include the original scores from games, remixes, compilations, and even Brawl original songs.
41 different stages including returning stages from Melee.
A stage builder letting you build infinite combinations of your own unique styles and ideas. Can be uploaded to Nintendo for a chance at Stage-of-the-day or sent to your friends over the internet.
Classic mode, a standard fighting game 1 match after another ascent to a final boss.
Event Mode, where the game sets you up in unique situations based on their own history and franchises for challenging matches such as Pokemon Battles. Co-op available here too.
All the types of Brawling: 2 minute KO Fest, Stock, Team, etc. Not to mention the Special Brawl effects (Giant, Metal, Spring, Super Speed, Super Slow, many more, and any combination of the above).
A total of well over 1,000 collectible trophies, stickers, and songs.
Demos of all the games the characters come from: Super Mario Bros, Earthbound, Fire Emblem, etc.
Many minor game modes: All-Star, Target Test, Home Run Contest, etc...
Screenshots that can be taken from any angle or character's perspective after pausing the game. These can be sent online to your friends.
100-Man Brawl, a challenge against hordes of enemies to see how many you can kill. Also available in co-op and online co-op.
Stage of the day, a stage builder stage submitted by people around the world will be sent daily to everyone in the world who chooses to download it.
Recordable matches, you can take recordings of your matches and watch them or send them to your friends over wi-fi, just like the screenshots.
Online multiplayer. Friend Code matches, random play matches, co-op 100 Man Bawl and co-op homerun contest.
