"It was the best of times. It was the best of times." - the Valve developers never cared much for the classics, but it's okay, because they do care about updates for Team Fortress 2, and there's a new one on the way. The Two Cities update brings with it new maps, new weapons, new achievements, and not very much Charles Dickens.
The first city: Mannhattan.
The first of our Two Cities, Mannhattan, takes our mercs all the way from the sun-blasted gravel pits of the Badlands to the urban sprawl of the East Coast, where they'll have to defend the manufacturing arm of Saxton Hale's boutique Mhankö line. Mannhattan's robot hordes can advance their own spawn points and introduce new bombs into the map for the first time, making for a unique new MvM experience.
Completing a Two Cities Tour of Duty will grant you a Killstreak Kit (transform any weapon into a Killstreak weapon), as wll as a fabricator and spare parts, so you can create your own Killstreak Kits, adding visual effects to your weapon and (eventually) yourself.
We also hear stories that completing a Two Cities Tour may potentially snag you one of the rarest items in the game: The Australium weapon - but we cannot say for sure.
As well as the new weapons and Killstreak Kits, you also get Snakewater, a new control point map created by community author Toivo Sawen, more in-game statistics than ever before, and confirmation that all the money your team collects on the battlefield will go towards unlocking a full Refund.
...what's that? You want more? Gotta wait until tomorrow.