Convert negatives to positives

Inverting the negative can create a somewhat flat image with low contrast.  As you can see from the histograms of the two versions of your Christmas photo, your image is more compressed:

One technique that will improve such a low contrast image is to use the Levels tool (Ctrl+L) or create a Levels Adjustment layer.   You can move the sliders on each end of the histogram to adjust the black and white points to the place on the histogram where there is actually some information.  And you can also play with the middle slider to improve the image to your taste.

Here you can see some improvement:

I have overdone it a little but I think you will see what can be done to improve the contrast.