If you're aware of Pikmin on GameCube then you should have a good idea of what Darwin entails already.
You start off playing as a chimp, and it's up to you to order other chimps around to attack prehistoric creatures, break down walls and carry back items to your base. Each level has a different theme (forest, desert, underground, lava, etc) and also an important artifact to find. As the game progresses the chimps evolve into cave-men and their weapons become more sophisticated.
The graphics aren't brilliant but the maps are large and there's plenty to explore plus you're able to stroll around taking things at your own pace. It's essential to re-visit already completed areas once you have more monkeys in tow, which adds to the replay value.
A nice little game, albeit one that could have done with a spit and polish here and there.