It's one of the joys of a new camera to see images that are noticeably richer (in a variety of ways) than the older body. I definitely remember seeing that after upgrading from D100 to D200 and then to the D300s and I really hoped to see it with the D600. I haven't been disappointed.
That being said I am still finding my way around the camera and in particular the autofocus. While up at the local ski hill yesterday I took a few shots of the family snowboarding. The moving subjects are great practice for when I go out with the hot shots. Not every shot was sharp by any means, but then with any body they rarely are.
But look at this image... this is an example of one that makes me just go WOW! The D600 is an awesome camera. The crop is 100% but the full image obviously downsized to fit this page...
Sometimes it's not just technique eg: the right shutter speed, lens etc... sometimes it can be the quality of the light that helps show an image in its best.. ummm light
As the others have said - you should post examples so we can see what you are describing. That's a huge help in understanding the problem and locating a solution.