Well, the map is opening progessively and there are nodes that make parts of the area visible but most of the time it's exploring. The map in general is rather huge with several levels connected to each other and it's always about finding a way to the next objective, while leaving some rooms up to explore for items and parts or collectibles. Sevastopol is pretty linear but huge nonetheless and that's why it feels so claustrophobic. The map plays an important part in the game.
It's a survival game so you have to use what the game leaves there for you. You constantly find useful things and gadgets/weapons that help you open up ways or new paths but it's challenging to handle all the encounters with the limited supply. The game lives from its atmosphere, the constant threat and clever level design.
. Anyway, everyone is entitled to their opinion...
