"Custom Robo" is a very difficult game to explain, but I will try my best to do so. It is basically an action game with role-playing game elements to it.
The Story mode... how do I say this? It sucks. This is the biggest downfall of the game. The game ACTUALLY forces you to play through this horrific, predictable story mode in order to unlock Custom Robo gear. The story basically starts off with the Hero wanting to join an elite group of bounty hunters. From there on, the predictability factor will overwhelm you, and the dialogue will make you sick to your stomach. That's pretty much all there is to story mode.
The graphics aren't all THAT bad. The battlefields (at least SOME of them) look pretty nice and have some detail to them. The Robo's themselves have a bit of detail to them as well. The framerate never slows down, and the battles maintain a fast pace. Though it doesn't push the Gamecube's hardware to its full potential, it's not too sore to the eyes. But Custom Robo's graphics are quite mediocre in this reviewer's opinion.
The sound? Ugh.
The gameplay itself isn't that horrendous. Your Robos start with 1000 HP and you basically use different Robos with different gear, which gives you some customization. Different guns, legs, pods, and bombs do different things. There are almost limitless amounts of customization to "Custom Robo".
The battlefields are cool. They give you the feel of virtual reality and can improve the lackluster experience. Believe it or not, there is strategy involved with "Custom Robo". You have to utilize your reflexes by jumping, deciding when to shoot, hide, dash attack, and whatever your heart desires.
Easily the best part of this game is Versus mode. Up to four players can dish out some heavy-duty damage to each other in a hectic battle. Arcade mode is simply a series of battles (similar to "Super Smash Bros. Melee"s classic mode). Unfortunately, you HAVE to complete the horrible, HORRIBLE Story mode to unlock the best part of this game. This is what truly disappoints.
Overall, it was an okay game, but nothing compared to a game such as "Super Smash Bros. Melee". If you MUST play it, rent it first. Not recommended.