To first get things out of the way, Valve are offering punters this weekend a free 2 day trial of TF2. The free weekend trial will roughly start around Saturday 03:00AM WST. Simply visit Valve's website here and follow the instructions. 

As mentioned, Gold Rush is the new map added to the TF2 line up which also features a new gameplay mode called 'Payload'.

The level is split into three separate areas with intermediate capture zones inside of each major chapter. The teams are split between offense (Blu) and defense (Red) similar to Dustbowl. The goal for the Blu team is to push the bomb payload through the level until it reaches the next capture point, eventually destroying all three of Red's major bases. Blu pushes the cart through the level by standing near it, with the cart moving faster when more people are close by. If no one has pushed the cart forward after 30 seconds, the cart will begin to move backward until it is pushed forward again. 

3FL have set up 9 new dedicated TF2 servers that are running the new Gold Rush map - for server and player levels check out the 3FL Server Spy.  

The Medic class is the first to receive the new array of achievements (below) which will eventually unlock 3 new weapons.

• The Blutsauger: a syringe gun which generates health upon hitting an enemy, this is unlocked by completing a 3rd of the new Medic achievements
• The Kritzkrieg: a new medigun which uses its Ubercharge to grant the recipient of the charge 100% chance to critically hit enemies, this is unlocked by completing two thirds of the Medic achievements
• The  Ubersaw:  upon taking damage through melee attacks, this will directly be converted to Ubercharge - four melee hits with the Ubersaw will be enough to fully charge whatever medic gun the Medic has equipped. This weapon is unlocked by completing all 36 achievements.

The 36 Medic class achievements

First Do No Harm: Play a full round without killing any enemies, and score the highest on a team of 6 or more players.
Quadruple Bypass: Heal a teammate who's taking fire from 4 enemies at once.
Group Health: Work with 2 other Medics to deploy 3 simultaneous Uber-Charges.
Surgical Prep: Have an Uber-Charge ready before the Setup phase ends.
Trauma Queen: Deploy 3 Uber-Charges in less than 5 minutes, and assist in 5 kills during that time.
Double Blind Trial: Deploy an Uber-Charge within 8 seconds of a nearby enemy Medic deploying his.
Play Doctor: In a team with no Medics, be first to switch to Medic after a teammate calls "Medic!", and then heal 500 health.
Triage: Deploy an Uber-Charge on a teammate less than a second before they're hit by a critical explosive.
Preventive Medicine: Block the enemy from capturing a control point with an Uber-Charged teammate.
Consultation: Assist a fellow Medic in killing 5 enemies in a single life.
Does It Hurt When I Do This?: Kill 50 Scouts with your syringe gun.
Peer Review: Kill 50 Medics with your bone saw.
Big Pharma: Assist a Heavy in killing 20 enemies, where neither of you die.
You'll Feel a Little Prick: Assist in killing 3 enemies with a single Uber-Charge on a Scout.
Autoclave: Assist in burning 5 enemies with a single Uber-Charge on a Pyro.
Blast Assist: Assist in exploding 5 enemies with a single Uber-Charge on a Soldier.
Blunt Trauma: Assist in punching out 4 enemies with a single Uber-Charge on a Heavy.
Medical Breakthrough: Assist in destroying 5 enemy Engineer buildings with a single Uber-Charge on a Demoman.
Midwife Crisis: Heal an Engineer as he repairs his Sentrygun while it's under enemy fire.
Ubi concordia, ibi victoria: Assist in killing 5 enemies on an enemy control point, in a single life.
Grand Rounds: Heal 200 teammates after they've called for "Medic!".
Infernal Medicine: Extinguish 100 burning teammates.
Doctor Assisted Homicide: Assist in killing 20 nemeses.
Placebo Effect: Kill 5 enemies in a single life, while having your Uber-Charge ready, but undeployed.
Sawbones: Hit enemies with your bonesaw 5 times in a row without dying or missing.
Intern: Accumulate 7000 heal points in a single life.
Specialist: Accumulate 10000 heal points health in a single life.
Chief Of Staff: Accumulate 1 million total heal points.
Hypocritical Oath: Kill an enemy Spy that you have been healing.
Medical Intervention: Save a falling teammate from dying on impact.
Second Opinion: Uber-Charge 2 teammates at once.
Autopsy Report: Provide an enemy with a freezecam shot of you taunting above their ragdoll.
FYI I Am A Medic: Use your bonesaw to kill 5 enemy Spies who have been calling for "Medic!".
Family Practice: Uber-charge ten of your Steam Community Friends.
House Call: Join a game that one of your friends is in and then deploy an Uber-Charge on him.
Bedside Manner: Be healing a teammate as he achieves an achievement of his own.

Source: http://www.steampowered.com/goldrush/