Unfortunately, I was only able to play this single person, however, I was still able to get the feel of the mechanics.
I think that the different abilities that the players have are pretty interesting, though I can't fully test them out without multiple players. I think the co-op speed boost is good and keeps players from splitting up, but I wonder if there could be an emerging strategy for splitting up, I would be curious to see that tested with playtesting. Though you would need to make changes to the camera setup. There could be another element that rewards the players for strategically splitting up. The UI for the monster's abilities is a bit confusing but the tutorial is very well done and walks the players through the controls well.
I was able to playtest an early version of this game and I think that everything that has been implemented is well done and gives the player a nice set of options. When I playtested the monster only had the phase through walls, I like the addition of another ability that can be swapped. The use of the middle mouse to scroll between the different abilities is intuitive and works well considering the limited inputs for multiplayer.
I really enjoy the overall aesthetics of the game. I think that the combination of the 2D sprites with the 3D environment is very cohesive and reads well. The lighting and particle effects add a lot to the gameplay and they gave me nostalgia for in-person games like laser tag, and the environment assets reminded me of playing manhunt. The dark mood overall is a good decision and makes sense with the hide and seek theme.
I can't make much of a statement on the multiplayer balancing, but I will say that as a player I think I would enjoy playing as either the employees or the monster.