I don't usually do this, but this game needs to be reviewed, because it needs to be made and it needs to be played.
I'll just put the TL;DR first. This is quite possibly the best RPG I've played since 1999.
The combat and character building is outstanding, and very balanced. There is essentially no filler combat, and the vast majority of encounters are really damn hard. The combat system uses a good variety of special attacks acquired through perks and appropriately rare single use items like special crossbow bolts, grenades or even caltrops to strategically tip the scales of a tough situation in your favour. Several encounters took me 3+ tries to get through. Cool downs between 2 and 5 turns make sure you can't just spam stims or a very powerful special attack to win.
Exploration is the second thing that stands out the most, along with combat. Stealth can get you places combat won't on several occasions, especially by using the black mesa developed technique of crawling through ventilation systems.
One of the areas you explore a few hours into the game stands out in particular to me, it's on par with genre classics like the Glow from Fallout, or Sierra Army Base from the successor. Those levels that are so well desgined that they feel like playing a Pen and Paper RPG with a good DM.
In a time where everything has to be a successor to something it's also really refreshing to see something do it's own thing. There's no "canon" to "break" for once. You've got your psi-abilities that reminds me of some PnP games I played a long time ago, a perk system reminiscent of Fallout, but with key differences, especially how you have to unlock things like aimed shot. Perhaps the subway civilization has also been done before. Despite all that it manages to feel really unique and innovative. For example, pretty much every single beast enemy you encounter has some kind of special ability, they're never just hit point bars with teeth. Even the equivalent of the Fallout rat sometimes comes with a leader of the pack individual that changes things up. The more difficult inhabitants of the caves will poison you as well as lay eggs that hatch more-than-annoying youngsters that swarm you at just the wrong time.
The game's economy also seems well balanced and interesting in terms of the crafting system.
If you like post apocalytic themes, turn based RPGs in the vein of the original Fallouts, that draw heavily on pen and paper rule sets, where your stats, tactical thinking and meticulous preparation matter and frantic clicking doesn't, you're sure to enjoy this game immensly.