I just spent forever looking for a pda cause I couldn't get thru a door in Alpha Labs 2. Turns out there was a ladder in the room next to it that took you to the pda you need. I was getting so pissed. That ladder is so difficult to see and took me like an hour to finally find it.
There was this one part where you are crawling thru a vent and this demon that appears for a second above you in this opening. That scared the crap out of me.