I played the web version, using the Vivaldi browser (Chromium based) on Linux. It did not seem laggy to me.
I was not able to release mouse focus when pressing escape during the game. I had to use Ctrl-w to close the tab. It would be nice if there was a menu to exit the game while playing.
I don't play this style of game at all, though have seen snippets of others playing some, so will give general feedback as best I can. The monster did not seem too scary. My first playthrough I was able to activate the points and exit without ever encountering it, though did see it in the distance a few times. I think the monster logic needs to be updated to expand its exploration area or otherwise be more of a threat. After winning I restarted and got close enough to trigger it to chase, then successfully got away. Finally I ran towards it. The monster gets you screen seemed OK, though was about what I expected and not that scary. This was a low stakes playtest for me, so maybe it would be more scary for someone more invested in a full game with others.
There was a building you could enter that initially looked like there was a wall, until you shined your flashlight on it and it suddenly changed to be an opening. The graphics could use some updating to make the entrance appear more distinct so the player knows where/what it is even if the flashlight is not aimed at it.
The activation min-games were all the same, so once I realized that it was quick to activate the others. A bit of randomness would be good.
It would also be nice if you listed the controls, even if just on the web page.
This seems to have the basics for the style of game as far as I can tell. It feels like a decent start.