I'd say Cubivore, Cubivore's gameplay is an action/adventure game with a few RPG elements in it. The purpose of Cubivore is to kill the Killer Cubivore's chronies, while at the same time attaining different mutations for your Cubivore. The ultimate goal is to attain 100 mutations, so that your Cubivore can become powerful enough to produce an offspring capable of fighting the Killer Cubivore. Thus, Cubivore is a game that is meant to somewhat represent the natural selection of humanity's evolution. (for more info, check out Wiki)
Not exclusive, but Killer 7 on the GC is better rhen the PS2 version