Custom Robo Arena is one of the greatest DS games out there, assuming you want to have fun.
The game's main aspect is the Robo Battles. These are fast-paced, action filled, and even strategic fights between two robos. These robos are completely customizable, and deciding on the right balance of parts is a key part of success. The other part of the game is the "RPG" story mode, which is kind of boring, but I kinda liked it. The story is mainly there to serve as an excuse as to why you're killing other robots. The battles become more interesting as you get further along in the story, you get an upgraded version of the Ray MK II, and later get more robos to customize.
The game also features WiFi battles for 2 players with voice chat for friends only.
Breakdown:
Gameplay: 9/10- The robo battles are fast and intense, but the RPG parts are kind of slow.
Graphics: 8/10- The 3D robo battles have some of the best 3D visuals on the DS, the RPG part has graphics that are worse than some GBA titles, but still have some strange charm to them.
Sound: 7/10- I'm not into metal, so I keep the volume low. The metal tracks do fit the mood of the battles, though. I kind of like the overworld themes.