If you want to be spoiled here is a list of all the changes I've found. (This can change at any time)
New Features:
The enemy AI has been improved. They seem to move around more and move again immediately after shooting even if they lose their targets. They will try to stay out of turret range.
New Weapon: Chain Shotgun. An extremely powerful but inaccurate automatic shotgun with pathetic range and fast rate of fire.
Damage: 20 (x3)
Range: 10
Accuracy: 40%-43%
Factions will be angry with your colony if they lose their people even if you didn't caused their deaths or they died by environmental factors (such as fire or temperature).
New Trait:
Wimp: Causes pawns to be downed after being hit once (regardless of damage) Reduces the pain threshold needed to be downed by 65[?]pp. Thanks /u/AllenWL
Enemy base generation has been improved significantly. Building contents will be hidden and they may have batteries, crops, turrets and more...
Special small encounter maps with veins of precious resources can be located using a new mineral scanner. The map however, may contain enemies who guard the resources...
Skilled pawns can dodge attacks based on their melee skill and their moving and sight stats. (Dodging is not possible when wielding ranged weapons). The maximum dodge chance without bionics is 36%, with bionic legs is 50% and with bionic legs and eyes 65%
New type of cover: Smoke provides 70% of cover and can stack with other cover bonuses like sandbags or walls to considerably decrease accuracy.
New drug: Ambrosia. A tasty fruit that increases mood and gives a short "high" but it is slightly addictive. A new incident will cause Ambrosia bushes to appear in the map.
Colonists can tend their own wounds and diseases!
Self tending efficiency x0,7
Pawn's heads are removed graphically if the head is destroyed
Quests:
A faction may request an specific amount of resources/items for delivery. This quest is timed and you will receive a reward when completed.
A faction may request the destruction of an enemy base. A new base will be generated with a new icon. When completed the quest givers will send you drop pods containing items or silver.
Roads and rivers added in the world and local maps
New Research!
Shield Belt: Allows the creation of personal shields.
Long Range Mineral Scanner: Allows the construction of the Mineral Scanner. They detect precious metals within 30 hexes of the world map.
Smoke Pop Belts. Smoke pop belts are a single use clothing item that create a cloud of smoke when a colonist/enemy is hit with a projectile creating cover and preventing turrets from locking onto targets.
Packaged survival meal. Allows the production of meals that can't rot.
Miners can fail to obtain resources if their skill is too low.
You can mass assign colonists to specific areas.
Waypoints can be added in the world map to show the estimated travel time to reach that location.
You can sort columns by skill level in the work tab.
New and updated floors
Wood floor Flammability 0 -> 22
Carpet floor Flammability 0 -> 32
[Stone] Flagstone floors added
Crop growth time increased. Growing heavily nerfed by ~40%.
Rice growth time (days): 2,4 -> 3,0
Corn growth time: 7,3 -> 11,3
Potato growth time: 3,2 -> 6,0
Cotton growth time: 2,7 -> 8,0
Psychoid growth time: 6,8 -> 9,0
Haygrass growth time: 5,0 -> 7,0
Strawberry growth time: 2,7 -> 4,4
New Graphical effects
Water now has reflections.
Caravan pack spot
New sprites for certain items (Like stone chunks)
You can find healroot growing naturally.
NEW HAT!
Bowler hats increase social impact.
Renamed the weapon equipment rack to "shelf"
Healroot:
medical potency 0,4 -> 0,6
Medicine:
medical potency 0,7 -> 1,0
Glitterworld medicine:
medical potency 1,6 -> 2,0
Seasons are now called quadrums and their names have changed
It seems ridiculously easy for wounds to get infected. Treating wounds outside increases the chance of getting an infection even more.
Factions button in new generated maps to check factions and their opinions.
Sun lamp power usage: 1'600Wd -> 2'900W
Sun lamps will be powered off automatically at night.
Injured body parts will now display their efficiency in the health tab.
Trade Caravan request cost increased: 600 -> 1'100 with low opinion, 300 -> 700 with high opinion
Renamed "Hate women" and "Hate men" to Misogynist and Misandrist.
Renamed "Research" to "Intellectual"
When treating wounds, doctors will prioritize the ones that cause more bleeding instead of healing at random.
If more than one colonist attempt to use two autodoors that are next to each other (like an airlock) at the same time, they will be slowed down significantly.
"Outside" is now considered to be a dirty room for cleanliness checks (Infections, operations and food poisoning)
When generating worlds with less than 100% coverage the area of the world that isn't generated will not appear black, instead it will be blue similar to the ocean.
More wild plants appear in the map, making it easier to obtain food early on.
Consciousnesses is not a health factor for most jobs and ranged accuracy. [bug?]
Drug production speed is now affected by the "Intellectual" skill.
Animal handlers with poor skill may fail to obtain milk or wool when shearing animals.
Added an option to hide hats in the colonist bar.
