Oh man, this game was just what the doctor ordered for the season! Loved the creepy atmosphere, and the topic itself never gets old! A few things I'd tweak personally:
1) improve rifle aiming;
2) add a hud;
3) add a level editor.
In the upcoming version, maybe add the ability to actually carry all the guns without replacing them, but as a balance feature - limited ammo, so the player has to switch between guns, naturally, gift boxes should give health and ammo pick-ups as well as new guns. Also, diversify enemies. The snowmen are fine and well, but surely you can add more kinds of snowmen (some that have ranged attacks for example), maybe add evil elves, naughty children, bad wolves, evil spirit-possessed-x-mas trees, stuff like that. Oooh, and some kind of holiday-themed weapon, or several: candy cane melee weapon, coal-shooter, snow-gun (ineffective against snowmen, of course), etc.
Man, if only I knew how to make my own game! :(