The reason I found the old X-Com games scary, and not so much the new one, was because of vision, it's always one of the reasons for Resident Evil as well. In the first X-Com and Terror From The Deep your soldiers could only see so much, the times that scared me were directly related to this. I would have a soldier go into a building, steps through the door, everything looks quiet, looks empty, okay good, calm breath, turn to the right to explore the door at the far end, as soon as my soldier turns - enemy, standing right next to them the whole time, just right there, face to face, those were scary moments. The newer one seems to have a bit too much vision for those old scares to pop up, not a horrible thing, just, that's one of things I loved about the old ones. It was also easy to get in a situation where your soldier is in a fire fight with an alien, to spend nearly all his points killing it, to then again turn and an alien is right there, or even have another alien appear in vision just behind the alien that was just killed. You have an alien trapped in a warehouse, you have soldiers guarding all exits, send someone around to blow a hole in the wall, you have two soldiers with them, to storm into the new "door" , but as soon as that wall goes down, there's a saucer on the other side of the wall, it turns and fires. Those situations just seem absent to me, and that's where the scare came from.
Same thing with Resident Evil somewhat. Where it can be attributed to the camera angles of old, you had many blind spots, where you heard enemies but couldn't see them. You'd have to make that effort to step into the unknown, then walk right into a trio of zombies, rush back, fire blindly into the unseen, then wait, and listen, are they down? are they faking? When they changed the camera they also, sadly, got rid of the majority of this type of tension scare. It's not impossible, you can easily have enemies around the unseen corner, or the other side of the door, only problem was enemies just ran at you, they wouldn't stay just out of sight ready to pounce, they wouldn't stay on the other side of the door and not try to open it, or anti-object collide through the door - What's that? An arm sticking through the door? Oh, enemy. For enemies to jump from around a corner when not expected, since RE4, it's all luck and player style. I saw it happen once, it was scary, it was funny, and it was amazing, but it' not something the devs put in there, it was a perfect storm of random, and the older REs did it on purpose, I give appreciation for the old ones for that reason.
What happened was, when I got RE4 I had a gamecube as did my cousin, so I played through the first disc, then he pulled another TV into the room, and his gamecube, then while I was on the 2nd disc, he was playing the 1st, that was pretty cool, same room, got to experience the game together (with only one copy of the game ^_^ ) anyways, he;s playing, first village area, first chainsaw guy pops up (I used to know it's name, Dr. ??? Salvador?), cousin runs, pops a few villagers, runs around a building, Dr. pops up swinging, cousin runs some more, loses the Dr. , gets into some trouble with some villagers, turns, runs from them. Heads down the side of a building, as soon as he reaches the corner a chainsaw sticks out from the side, and clotheslines his head off.