(Made to avoid necroing the other Xenonauts 2 topic from ~2017 and so I can update this as things change. I can always lock this if it's deemed unnecessary.)
Xenonauts 2 is, well, it's the sequel to Xenonauts 1; the fairly successful spiritual successor to X-COM UFO Defense taking a more traditionalist approach versus other more radical interpretations of the time, such as the Firaxis-developed XCOM.
In terms of
setting, it's similar to but quite different than the first game: it's a alternate timeline where, thanks to subtle alien interference, the cold war continues to modern day where the game is set. It's focused around more of a "shadow war" between the Xenonauts and aliens to reinforce cold war paranoia, and takes place immediately after the Xenonauts lose their main ground base to an alien attack and are forced to evacuate to a hidden base in Iceland.
The combat side this time around is rendered in full 3d, rather than 2d like the first Xenonauts.
The following information comes from
this thread on the Xenonauts forums, which is generally accurate but subject to change as development isn't yet complete.
Regarding the Geoscape:
One point of the game is the doom counter DEFCON system, representing the loss condition. The aliens attempt to raise it to get the world destroyed in thermonuclear warfare, and you try to keep it low so everyone doesn't die. There's also a threat meter that fills up, representing how concerned the aliens are about you; once it hits 100%, a base attack is triggered (which is a set force) that you have to win, or else you lose.
Relations are redone, with a single meter representing both alien infiltration and a region's attitude towards you. It's a 10-pip bar, with relation points being green and coming from the left, and infiltration points being red and coming from the right. If infiltration level is double that of relations, then you lose the region. Field Agents, a new mechanic (similar to covert ops from XCOM2 and XCOM1) allow you to manipulate this without direct combat encounters.
Readiness represents the maintenance level of your base's helicopter, and is used to moderate the amount of ground combat actions you can do in a specific timeframe. It can be increased through means such as assigning extra engineers to maintenance, but is generally used to avoid players feeling the need to respond to every situation ever.
Operation Endgame is your victory meter, and is increased passively by your chief scientist, but can also be increased via assigning more scientists, certain research projects, and other actions.
You have a single base, amusingly similar to Firaxis' XCOM1 and XCOM2 bases. This is the only base where you store items and personnel, and you have to manage things such as upkeep and power. Personnel (such as scientists) can be assigned to specific rooms for certain effects, and the entire thing is done via an "ant farm" view -- again like the Firaxis series or, for those of you unaware of Firaxis' base management, Fallout Shelter. You have auxiliary bases to house interceptors and the like (and radar coverage is just purchased on a region-by-region basis). Also amusingly, base defense missions are done in a premade layout representing the command area of your base. Like the base defense mission in XCOM1.
While alien alloys plays a similar role in Xenonauts 2 in the resource category, Alenuium takes a different form: Alenium Cells. These aren't actively consumed by anything, but rather restrict the deployment of certain high-tech items. For example, deploying a laser may require an available alenium cell, meaning you have to budget them appropriately. An example given was that a laser could be more damaging but would also be requiring Alenium cells, with coilguns being less effective but requiring no cells.
Air Combat is now just an "advanced autoresolve" with the tactical portion removed, currently. Your interceptors have the ability to do a single high-speed attack run on the UFOs, then they retaliate doing the same thing.
Soldiers now rely on both experience and training. A soldier could have an accuracy stat and a set level in "Rifle Familiarity" affected by in-base training that would only have any effect on the accuracy of rifles.
The reason for posting this now is that their
Kickstarter just launched. As I type this it's already gotten past its funding goal, but the game has a decent number of stretch goals and rewards that people may be interested in.
There's an Alpha Combat demo available for download as well, linked in the kickstarter.