I think this is a bit of a hidden indie gem - allow me to elaborate.

Technically you get two different games in this package. The 'story-driven campaign' and 'open-world exploration' are separate modes, mostly unrelated to each other. I personally much preferred the latter - both are enjoyable, just for different reasons.

Campaign:
- pays homage to Half-Life 2 and you can expect this manner of gameplay and level design here - physics shenanigans included,
- linear, with a clear story and direct, obvious objectives to follow,
- sweet and short, can be completed relatively quickly.

Exploration:
- pays homage to S.T.A.L.K.E.R. instead, it's slower paced and more atmospheric, with a dynamic, much less scripted world,
- embark on expeditions from a specific starting point, learning more about the exclusion zone as you go,
- there are some scripted missions you can unlock after finding specific locations, but otherwise you have a large multi-area world to explore with one grand objective and little in terms of directions on how to get it done,
- you are given room to take notes as you see fit and it's your job to explore the world, write down anything of interest, find out what secrets it holds, solve puzzles, connect the dots, follow the clues and potentially pick up other objectives as your intel on the area increases
- collect artifacts and curios to pay for and unlock more gear, as well as find upgrades out in the world,
- unlock potential companions through missions and actions in the world (you can opt to take one with you or go in solo, there's also areas companions cannot follow you into)
- there is no hand-holding and you can absolutely get stuck not knowing what to do, information available online is also pretty scarce due to the game being rather niche, but it feels rewarding to progress
- learn to navigate a hostile world filled with anomalies,
- day/night cycle, atmospheric events including anomalous storms not unlike the blowouts from S.T.A.L.K.E.R. that force you to seek cover,
- wide variety of enemies and environmental hazards to keep you on your toes - while generally the difficulty doesn't seem to be particularly high, there are times and some particularly dangerous enemies that will catch you completely off guard - you are never safe,
- honestly, it gets pretty scary at times. There were a few areas I dreaded going through every time just because they made me uncomfortable (in a good way, of course).

Is it flawless? No, the story of campaign mode didn't exactly captivate me, though I still had fun playing through it. However, being an avid S.T.A.L.K.E.R. enjoyer, I had a great time digging into the mystery of Exploration mode and found myself playing it for about 25 hours before reaching the ending and I didn't even get to enter the power plant at the end. There seem to be multiple endings based on completion of your exploration, though not exactly much variation to it. You're allowed to continue playing and finish all leftover objectives afterwards, if you happen to, like me, reach it before finishing absolutely everything else.

The dev is also making a new game called Project Silverfish, which seems to take plenty of hints from the open-world mode of ADACA, set in a fully fledged post-apo setting and if, like me, you also find the idea compelling, I recommend taking a look. I'm definitely interested after what I got to experience here.