Brawl is what make the Wii what it is!
The combat system is practically identical to the previous iteration. While this will excite hardcore fans, players who never got into Melee will find little here that will change their minds. The nunchuk/remote control option is completely serviceable, but you're really going to want a GameCube or Classic controller to truly succeed. The sideways remote-only control scheme is a complete mess, and should only be used to put friends at a hilarious disadvantage.
Outside of alternate control options, the biggest change to core combat is the Final Smash. These icons randomly float through the air and encourage players to drop what they're doing and go for it. The first to grab it can unleash a satisfying overthetop, screen-filling attack that may turn the tide of battle. Final Smashes do not, however, guarantee victory and can be turned off in multiplayer for concerned purists.
The dozen-plus new characters bring a little something fresh to the fight and are balanced well with the rest of the roster. Pikmin tamer Olimar gains stronger attacks as more little friends follow him around, Metal Gear's Solid Snake has a steerable Nikita missile shot, and Sonic utilizes his trademark speed in interesting ways. However, characters like Fire Emblem's Ike, Zero Suit Samus, and Mother's Lucas are slightly tweaked palette swap replacements of existing or former characters. It would have been nice to see more reimagined classic characters like Pit, but it's tough to complain when there's already this much variety.
New clever stage design is where you'll find most of the innovation in Brawl's battles. My particular favorites include arenas based on the constantly changing environments of WarioWare and Pictochat, and the side scrolling world 1-1 of the original Super Mario Bros. With the constant stream of unlocks, it always feels like you're getting a fresh backdrop to experiment in.
While Classic, Event, and Stadium modes return in similar form, the centerpiece this time around is the Subspace Emissary. This seemingly endless barrage of platforming stages and battles joins together the cast for one giant war against a mysterious enemy. An absurd amount of impressive pre-rendered cutscenes ranging from epic to just plain silly tie everything together, and will most likely be the primary incentive for many players to make it through the entire campaign. Essentially a 10-hour Classic mode, this adventure gradually loses its promising luster through repeated environments, challenges, and enemies. Like most games out there, however, playing co-op style helps keep things fresh.
Online play is implemented about as well as it can be within Nintendo's structure. After going through the friend code hassle, Smash buddies can be easily browsed to see who's online. Friend battles include basically all the options of the offline mode, though true voice chat is disappointingly replaced by customizable phrases mapped to the d-pad. Facing off against strangers, however, is a different ballgame. You can't see anyone's name, communicate with them in any way, or customize your match outside of item toggling. Everyone's so devoid of personality that it's almost like you're fighting bots. The only match type available is a "2 minute KO-fest." No time options. No stock matches. The only thing you can definitively choose is your character.
Outside of the need for online improvements and a more concise and engaging campaign, Brawl still hits all the right buttons. With extremely tight controls and finely tuned balance, the core fighting mechanics and local multiplayer are spot on. There's still nothing like learning the intricacies of every character, discovering possibly the most unlockables in any game yet, and using all of that to beat the crap out of your friends late into the night.