January's big Guild Wars 2 game update will be Flame & Frost: Prelude, arriving Monday, 28th.
It's a prologue to a multi-stage narrative that "will bring big changes to Guild Wars 2 in the months to come", according to the official website.
Broadly, Flame & Frost: Prelude will bring daily achievements, new achievement rewards, new Ascended items and Infusions to spend those rewards on, and a week of paid tournaments on PVP map Temple of the Silent Storm.
Lead game designer Colin Johanson talked about a few of these things in his year-ahead post last week.
There are new items headed to the Gem Store too, including Quaggan Backpacks, Riding Brooms and a revamped Box o' Fun.
Guesting also arrives in this update. This lets you visit people on other servers in the same region without changing your home world. It's free, but transferring servers (after 28th) will cost you gems.
On top of all that new stuff, ArenaNet will improve world-versus-world game performance, better balance side-kicking and improve the user interface.
No doubt there will be professions tweaks as well, but all that mumbo jumbo will have to wait until the detailed patch notes are released.