D7000 Photo Format on LCD

I have been thinking about this for some time now. I would think is the same in other Nikon bodies, but when you take a photo (mainly in JPEG) the photos LOOK really awesome overall and i personally get very excited after seeing such "result", but when you load them onto your computer they do NOT look the same at all and the feeling is more disappointing with the expression of:  "WHAT DA HECK???"

The image being displayed on the camera's LCD is it perhaps a RAW format or a different kind of high quality format, or is it just simply what my eyes are seeing due to the fact that it is in a 3" little LCD??