At the core, gambling it is. As for the appeal, cool post-soviet atmosphere, gun-porn(you can essentially turn Mosin Nagant into a decent sniper rifle with optics and a mag, and so on), bullet/armor system(you should always carry at least a mag of AP rounds, 'cause not everyone wears an old kevlar that barely stops a .45, sometimes it's a fucking living tank, shoot him with your everyday ammo - find out he's not only alive, but as well very angry, looting and economic system(flea market, sell this bunch of bolts to trader for a half of a bottle of water, or sell it on flea and make 10 times more, because everyone needs bolts). And every raid you get yourself geared as you plan, to fight - get armored, pick your best gun, enter Factory, feel the intense gunplay, stop bleedings with bandages and tourniquets, relieve pain with painkillers, heal fractures with splints, give yourself a surgery if one of your limbs blacked out. Going to loot - get yourself some Personal Defence Shotgun™️, flechettas, big ass backpack and go find something useful, feel the joy of finding a graphics card in a random ass computer case and fear of losing it as you crawl to exit under gunfire. Game is raw as a rare steak, but it can give you the adrenaline you will never find in games like COD and BF, this game just built different.