Super Smash Bros Melee is the must-have for any GameCube owner and is the ultimate multiplayer fighting game.
The gameplay is amazing. It's very easy to pick up and play, which makes it approachable for people of all ages. Also, there aren't any complex combos to remember, like other fighting games. Items from Nintendo franchises, such as pokeballs, home-run bats, and warp stars can be found strewn about the stages, which makes the gameplay so much more interesting. With one item, the entire momentum of a match can change.
The sounds of the characters were provided by each of the character's real voice actors, and Nintendo didn't give any characters voices if they did not previously have them (Samus, for example, does not say a word). For each stage, the proper song played (a Mario theme plays on a Mushroom Kingdom stage). It added to the feeling of each stage, making it feel like you're really fighting in the middle of an F-Zero race, for example.
But the value of the game is were this really shines. There are several game modes to choose from, such as story mode-like Adventure or Classic, or Event Match, where you are given an objective to complete. Of course, there are other fun modes, like Home Run Contest and Break the Targets, but you will probably get the most playing time out of Vs mode. You can set the characters (or add CPU players if no one is around to play against), items that appear, lives to lose or time to count down, and of course, the stage to fight on. You are given many options to customize your matches, so you never tire of just one setting.
You begin the game with only a handful of characters, but playing lots of Vs matches (every 100 matches unlocks a new character, if you can beat them) can get you more fighters, like Dr. Mario and Ness (Earthbound/Mother). And playing through Adventure, Classic, or Event Matches get you coins. You use those coins in this vending machine, of sorts. You put some in, and you get a trophy. Each trophy has something to do with Nintendo, from predictable ones like Mario and Kirby to obscure trophies like Ridley (from Metroid) or a Metal Box (Super Mario 64). It's not like there are only a few trophies, either. The total count is upwards of 350.
To sum it all up, Super Smash Bros Melee is one you definitely can't miss on the GameCube. The gameplay is great, the sound is appropriate to each stage, and there are a tons of things to keep you busy, from breaking targets to collecting various trophies. You're a fool to miss a masterpiece like this.