This game is basically a scavenger hunt on a partially procedurally generated map (the layout of some areas and the locations of items change, but the "big picture" remains the same), except there's a monster coming after you. This monster will kill you very much if it finds you and it can't be killed.
So, you move from room to room looking for the items you need to escape, hide in closets when you feel danger is close and occasionally bump into the monster and run like hell in the opposite direction. The monster is constantly seeking you, and will eventually converge on your location (yes, it "cheats") so you have to keep moving, but you can use some trickery to get the monster off your trail temporarily. There are 3 different monsters (but you only face one per game), each with unique mechanics.
Once you find the needed items, you head to one of the escape vehicles, install the parts and then trigger the escape sequence and fend off the monster until it completes. Once that sequence completes, you escape and win.
This is a horror game, but the horror element is pretty "light" in my opinion. It's not absolutely terrifying, but it's still good for a bit of an adrenaline shot.
Each run normally lasts around 15-30 minutes. Though, depending on random, you may find yourself wasting an hour trying to locate key items or find everything and escape in like 5 minutes. That's random for you.
As for replayability, I see this as the sort of game you occasionally pick up, play, and then put back on the "shelf". I don't play this every day, but come back to it once in a while when I'm in the mood.
All that said, this game still feels more like a demo of what "could be" than a full game. The overall concept is pretty solid, and the game is fun (assuming you like this sort of thing), but it is definitely begging for more monsters, more maps, more items and a bit more polish in some areas. On sale, it's an instant buy in my opinion. But at full price I'm not so sure.