Raw files, by definition should be shown as an image with no processing applied. But then you would not see anything. So a really poor looking image could just mean that your other application does more twiddeling with the raw file than Aperture in order for it to be visible.
Set up your own Raw Image Standard/Datum Point; Import a typical raw file. Apply the adjustments to get to what you think the image should look. When it is to your liking go to Presets, at the bottom of the drop down list is the option Save as Preset, click it, now name it in the window that just opened. Call it Raw Tweak or whatever. Click ok.
Now when you import, go to the Adjustment Presets and choose Raw Tweak. That will be applied to all your imports as long as it remains selected. Powerful Stuff !!! Welcome to Aperture. Allan