The new game menu has been modified. You still enter your player name and then the package you want to play (just like before). However, after this you are given a list of options. The first option is to start a new game. Another option is to change the "starting configuration". Another option is to change the seed. Then, the remainder of the options are to set variables that are passed to the package. We call these variables "mutators" See the guide on how to add mutators to your own standalone package (if you are a modder).
The standard xar package now has the following mutators: "One Way", "Low Ammo", "Low max ammo upgrades", "Low upgrade buying", and "No stable singletons room". You can read about what these do in the new game menu.
Now some of the Williston Fields at the base of Williston Trees (in I1) have orange cubes in them. These cubes contain Cannon Max Ammo upgrades. Let's call these "rich fields". Rich fields inside larger rich fields are even better, etc. This gives a reason to shrink several times in Williston Fields.
The Great Mylantis Cavern has been added to. Now there are many small boats as well as one large boat called "The Mount P". These boats contain two new super weapon modes for the Cannon weapon: "The Sheriff" and "The Judge". Try "going fishing" for Trolls in the Great Mylantis Cavern using The Judge. If you have an old waypoint in The Great Mylantis Cavern, then it will no longer be valid (but you can go back into the cavern by using the cheatcodes noclip and shrinkany).
Ultrawide monitor support is in beta.
As a modder, there is now a way to synchronously cast a ray into the world and get what block and moving entity it hits.
There is now the environment variable "engine.exit_on_deprecated". When this is true, the program will exit whenever the package uses a deprecated API function.
It is now easier to pass information to and from procedural world generation code.
The waypoint system is no longer hardcoded into the engine. That is, the engine no longer has any concept of what a waypoint is. Instead, the waypoint system is written in Lua as part of the base package. This makes it much easier for modders to create their own waypoint system (or modify the existing system).