A fantastic game. Has everything you need to enjoy great single-player and amazing multiplayer experiences.
Single-player has a variety of modes you can choose between, some of which must be unlocked. Classic mode is your basic "choose a character, smash things, win" set-up, and allows you to get your first set of character trophies. All-star mode becomes available once you unlock all 35 characters, and can be played with a friend. Its more of an endurance challenge, having to fight all 35 characters in a row, with limited healing items.
The Subspace emissary is a fantastic game-mode. Whilst relatively short, even on the Intense difficulty setting, it provides an interesting twist to the Smash Bros. Series; a Plot. As I said above, its very short, but can provide a couple of hours of enjoyment (with a friend if you want).
But Brawl really shines in its group modes. The default Brawl is a fantastic mode, which lets you play with up to 3 of your friends, and if you don't have enough friends around at one time, you can put in CPU controlled opponents to brawl with, with 9 levels of difficulty.
Online play is a refreshing new feature. You can play with friends or with anyone. All names are hidden, which can be both a blessing and a curse.
The stage builder is a great little addon, which allows you to make your own stages. They are quite basic, having no events, but its great none-the-less. In addition, you can now save replays and snapshots. A handy little function that many use.
The online Smash Service provides you with 1 new stage, replay and snapshot everyday, giving something new to try each day.
Overall, Smash Bros. Brawl is one of the greatest games ever made. It has massive replay value, and its unpredictability means no two matches are the same.