So the gallery is unlocked after defeating the plant boss. I had to use the "ResetMainMisson" command to get it to activate the bossfight. pasue the game, click on her head, type (i copy and pasted) the command, save the game(if you used the save file you should be next to a save point), exit level, reenter the save you just made. after being the plant boss, talk to the girl and it will unlock the gallery.
Overall I really enjoy this game. I think the animations are amazing and its relly caught my attention so far. after seen the current end of the game, i can tell that there is still so much instore for us in the future. we have barley hit the tip of the iceberg. besides a new monster or two the levels can get a bit bare. theres is little for you too do other then shot or die. I like the interactive parts of the game, tentacle door, horse, and hope to see more of that in the future, maybe with more impactful or meaningful consequences for your actions. 8.5/10
PS, I still dont know how to find the Christmas level(if there is one) in game, only in gallery