Techno/Supernatural Thriller
Assuming you stick with GURPS, I'd probably drop point values to 100 or 150. 300 is a lot for a "normal" person, unless you're going for super-competent FBI agents or something. If you play things out episodically, it can work well to start at 100 point for Suzy the Secretary, introduce the bizarre circumstances, and then give a big slug of points to allow Suzy to adapt to the new reality and all of that.
My warning on adult is that a lot of stuff with gore, corpses, and the like can verge into adult material pretty quickly. "Adult" is not the same thing as "sexual" (though that can be a reason for it to be adult). You're almost certainly going to end up in the wide grey area between "mature" and "adult", per the rules, and it's usually better to err on the side of caution.