I like it how you don't have so many forums, and so for new members, its easier for them to navigate, and have a lesser chance of placing a topic in the wrong forum.
Good color scheme for Christmas. Its not a contrasting red, or green, instead a rich dark red. Good on the eyes 🙂
Pretty nice lot of statistics. People tend to like bigger amounts of posts, and lesser amounts of members, but not too less. You have a good ratio of posts to member's, and a good cohort of staff. They seem to be fairly active, and log in.
Dislikes:
The site could do with a background. Just having the white is a bit plain, and it "radiates" in your eyes when scrolling down.
The banner has already been mentioned.
You seem to have the majority of posts, so if users see that, it can make your forum appear not as active, as they want it to be. Try to allow members to breath, and give them a day just for them, even if it means you not posting at all. Its a forum for them, not just for you.
I'm not too fond of the small Christmasy icons. I know you want it to appear like Christmas, but some are quite random.
I had a little trouble finding the register button. Try to make it stand out from the rest.
There is just nothing truly unique about your site. Have a think to yourself, why would someone join your site, and not a fully developed site?