This is honestly the most wholesome flash game I think I've ever seen on this site. It works really well at getting you into that Christmas feeling, with that cozy music and the snow slowly falling down, next to that giant, undecorated (as I'm typing this) tree.
The gradual adding of classic Newgrounds characters is also really, really appreciated. I don't speak for everyone on this site, obviously, but it's always nice to see Pico, Captain, the Madness grunt, and that goddamn clock inside of a strawberry. I really like the detail of the snow sculptures representing Behemoth, it's really sweet. Additionally, I think it's awesome that a bunch of artists got together to help make this happen. Newgrounds has always had a pretty great community, and there's no better time to show that than the holiday season. All the art pieces are great, I think my favorite one so far is SuperPhil's festive picture of Salad Fingers and his merry gang.
Only caveat I have is a minor one that'd probably be difficult to add in; it'd be really cool if you could interact with the characters in some way. Even just tiny things, like having a chat bubble showing what they want for Christmas, or what they got when Christmas rolls around. It's not a severe flaw by any means, just a "mite b cool" type of thing.
I'm gonna keep checking this out for the next 19 days, it's really endearing. Hope everyone has a merry Christmas when the time comes!
Update for 12/25/18: It's here! MERRY CHRISTMAS!