I'm not going to claim I pay any real attention to it in my own work, but one thing strikes me.

I have no idea where the light is coming from in the picture there.

The characters seem to be lit from above, and/or towards the camera. The cylindrical hatbox from the right, but it's shadow from the left. The box matches it's own shadow, but seems lit from above and to the left, somewhere past and behind Santa.

However, shading weirdness aside, the colours are good, and it really brings it all together nicely, I get a much stronger sense of "Oh, you!" from Santa.
Also, best present.