Late last night (if you're reading this on November 22nd of 2013), the TF2 team at Valve has released an update called the Two Cities update. This update gives Mann vs. Machine some love. MvM has generally been neglected by Valve for some time in terms of TF updates, and this update comes as a pleasant surprise. The size for this one is ~450 MB, so it might eat into your bandwidth for a while if you haven't already downloaded this update. There's a lot more stuff to go through, so here goes:
Snakewater
Widely played especially throughout the competitive-oriented TF2 community, Snakewater is a 5-point capture point map made by Toivo Sawen. It has long been in many public server rotations as a custom map, and its inclusion in the game means that you can finally clear up some space off of your HDD/SSD in case you had several iterations of the map (before its official inclusion). The map also comes with its own set of achievements, which has been the trend for most custom maps added within the last year, though there are some notable exceptions.
As with other custom maps, map stamps are available, so if you want to support Toivo Sawen's efforts, it'll only cost you a dollar. Want to show more support? Buy more map stamps for Snakewater. You can buy said stamps at the Mann Co. store through the online store, or in-game. The map's creator is also currently hosting an AMA question session on reddit as well.
redditor omnibombulator has interestingly pointed out that some of the map's details are not the same from before the map's final inclusion, of which omnibobulator has prepared an imgur album.
New MvM Leaderboard HUD
For stats junkies out there, Valve has added a more detailed MvM HUD scoreboard. You will now be able to see who's done what, and how much money each player has. If someone isn't doing enough damage to tanks, speculation on who isn't doing enough is no more. The era of reliance on server plugins for these stats is now past us as well.
New MvM Upgrades
Valve's TF2 team has also given the Medic even more love in MvM as well. Previously regarded as a "useless" class, these upgrades will turn those views upside-down. The Medic's role is now even more expanded, as he can now bring dead players back to life, greatly reducing the need to spend valuable money on buybacks. He can also now block projectiles as well, which could easily become devastating combined with an Engineer sentry nest. Soldier also has a new rocket specialist upgrade, which will increase his overall damage per second potential with direct hits.
Rottenburg
A bunch of new upgrades couldn't go without a new map. Based on Medic's hometown*, Rottenburg becomes the fifth official MvM map in the game.The lore states:
"The second of our Two Cities finds the mercs defending the Medic's vaguely European hometown of Rottenburg — a sprawling village famous for its centuries-old traditions of 1) chasing the next in the resident lineage of mad doctors out of town with torches and pitchforks whenever they swapped out too many super-charged baboon hearts, and 2) never having been attacked by an army of robots.
Everything else...
There were also a plethora of other changes, far too many to list here for space purposes. You can find the rest of the changes on the Steam store here: http://store.steampowered.com/news/11931
The "Paper Toss"
For a long while, fans of the TF series and its lore have been complaining about Valve's lack of content updates, but in the last few months, Valve looks to be picking up the slack. It's only less than a month until what should be the Australian Christmas update, and what it will bring is up to your imagination for the moment.
I still don't have an ETA about the sequel to "Ring of Fired", as it appears the creator (through a Tumblr post) stated the sequel hasn't been finished just yet.
As always, you can find me on reddit, Facepunch, and the Steam forums (where I cover various updates for various games other than TF2, such as Dota 2 and CS:GO), or on Twitter as well.
* A discrepancy has arisen with the update, as the Medic's class page has his hometown still shown as Stuttgart, Germany (though this simply could've been a birthplace). Until this is clarified, this is pretty much free speculation material.