I love Photoshop! Using the right tools can yield amazing results, significantly improving and oftentimes saving an image. Photoshop is our modern day digital darkroom.
Look at the photos that follow. Though the first image, our "Before" image, was underexposed, there is still some detail coming through in the shadows. Remember, while Photoshop is a great tool to have, it cannot save an image that has no information in the highlights or shadows.
Now, look at the second image. Exposure was adjusted using a levels adjustment layer, shadows were opened up, highlights were brought down slightly, a bit of contrast was added, lines were straightened and the image was color corrected.