Organize photos, edit metadata, adjust colors, saturation and other properties.
We could stand out some advantages in Aperture:
Support for RAW files of the main manufactures, including Canon and Nikon, so you won't have to change format before working on them.
Non-destructive process: Aperture keeps the Master image apart from the one which is being modified.
Flexible image management: You don't have to import imaes into Aperture to manage them. You can link them in an easy way.
Comparing it to iPhoto, Aperture uses projects to group photos. You only have to access 'All projects' in the 'Projects' tab to preview all images in it.
Finally, Aperture allows yuo to apply lots of exciting effects on your photos. Fine RAW adjustment, Exposition, lights/shadows, levels, white balance, red-eye reduction, cut, crop, resize,... All those functions and many more are in Aperture. Give it a try.