im currently playing it as well. din knew it was such gooding until i delve deep into this 

yes. until i go to youtube to find that Rifle and trick to kill it.....
its damn satisfying and i agree that sweetfx makes the whole graphic thing more darker

you remmeber the big HALL? 2nd floor, or level 3.
c your mini map properly and try every door
*you at ground floor - a BIG stairs at the hall. go up 1 floor, and your mini map change, got 2 door at SIDE. go either 1.
then at 2nd floor, there's only 1 door in your mini map. go all the way until you reach the pool, then got 1 door at the end of other side. inside got the rifle and undrain the pool (come bac later watever it means coz i aint back to it yet at chapter 4).
i'm still enjoying it slowly in which a chapter take me an hr. scan every corner/room/place 

yeap. door tepi ada circuit....so go near the circuit and press A/X. then Jill will unscrew it and complete the puzzle