WRONG. It's actually an unbalanced mess. At least, that's what a group of Smash Boards members seems to believe, seemingly with more conviction than we've ever had for pretty much anything. It's important enough that they decided to patch the game's code to change specific gameplay elements. "Balanced Brawl" has three goals, as stated by the coders: first, to remove "infinites" and "inescapable lockdowns" (simple, unblockable combos that add more than 50% damage), increase overall character balance, and increase stage viability.
You can see examples of the kind of minute tweaking done to the characters in the chart above, and you can read way, way more about each change in the Smash Boards thread. It's a pretty impressive testament to just how much time has been spent thinking about Brawl.