Love the simplicity of this concept, you've made a very fun game. Just a few opinions of mine - apologies if you've heard these from others already:
- Bodies should not despawn once the bacteria has killed them. Would add to the atmosphere and also not interrupt immersion when they suddenly despawn in front of you.
- Smilers should be something to avoid. They're pretty passive and there's no reason to fear them. Maybe they could 'stalk' the player by following and moving closer when not being observed (like in the game 'bulldogs')? How about a debuff like affecting movement (dizzying effect, slowing movement etc) or 'crippling' the player in some way?
- the hiding holes are a bit corny, they look too... "intentional". Perhaps some features that look more organic and inkeeping with the lobby aesthetic? Maybe, areas where the dampness and mould in the level has caused the wallpaper to bubble and peel away, and rotted through the boards underneath, exposing a crack large enough for the player to crawl inside? To me, the map needs voids to hide in that do not interrupt the liminal space but also do not look like they were added simply for gameplay mechanics reasons - they should fit the aesthetic theme.
- a way to leave 'breadcrumbs' - players should be able to drop a limited number of markers to aid navigation. This would allow the levels to be even more expansive.
- the bacteria charging at you could have environmental effects, like causing the lights to flicker, to add to the visual drama.