I personally don't mind the snow effect; the opposite actually. It's charming and adds a particular vibe to the forum, especially since it felt rather stagnant before the change. It is seasonal in nature, so I doubt it'll be around much longer than the end of December anyway. If I had to criticize anything, it'd be the snow PNG overlay on the icons. I see what they were aiming for with that, but it's somewhat a sore thumb on certain avatars. But again, it's still charming nevertheless. Funnily enough it somewhat makes my icon look like she's wearing a Santa hat with the white rim and red top. Haha.
As far as the characters, I've never watched or read One Piece, at least not thoroughly, but I'm at least somewhat aware that Zoro is among the main cast; well enough to justify a bit more than being a "random side character." But it does seem odd, to have him rather than Luffy among the prominent main characters. He looks sharp though, and I imagine he's a fan-favorite, so it probably suits better for appearances than the alternative.