Extracausal is a lush, intense, Trophy-system game about interacting with a vast and interconnected occult. Its art is bleak and atmospheric, and it takes notes from the I-can't-honestly-say-yet-whether-it's-mainstream-or-a-cult-classic game Control---but it might just as easily work as a lighter conversion for something like Unknown Armies or Delta Green.
Extracausal is 29 pages, and it's got a fair bit of text, so for a short game it's going to feel hefty. However, it's also self-contained, so you don't need a copy of Trophy to play.
You *do* need to have played/run other trpgs before, since it assumes you've already got a strong grasp of the fundamentals, and this might potentially wall out some people who would otherwise be interested in the SCP vibe of the game.
Mechanics-wise, Extracausal is well-tuned for suspense and horror. You generate a pool of dice by invoking elements of your character, and certain elements when invoked complicate a scene. Getting dice from injuries makes those injuries relevant to the scene. Getting dice from the supernatural makes it more likely to intrude and overshadow you. It's neat and atmospheric, and leans just to the storytelling side of being gamey and crunchy.
One thing not really featured in Extracausal is sample mysteries, monsters, agencies, etc, so you may want to bring your own mythos to the table if you're not confident in your ability to freestyle a gigantic conspiracy during the first session.
Overall, I'd recommend this to anyone who likes X-Files, or any of the other media I've mentioned so far, and who wants a story-first game of suspense and occult horror. If you're looking for the same, but crunchy, this is probably not your jam. And if you're looking for a prepackaged setting, this doesn't provide that. Otherwise, I absolutely encourage you to check it out.
-Apcoalypsis and Tenebrae being able to be set back feels like it bleeds out some of the tension from the game. At the same time, the vagueness of when to advance those tracks makes the escalation of tension feel a little arbitrary. Maybe tying them to choices at the end of modules might help? "If you did W, gain Apocalypsis and lose X", "if you did Y, gain Tenebrae and gain Z."