Games like Darkroom
Games like Darkroom include Firewatch, What Remains of Edith Finch, The Beginner's Guide, Among the Sleep - Enhanced Edition, and Layers of Fear (2016). We matched them by the tags players give Darkroom on Steam (Indie, Short, Adventure, Horror, and Walking Simulator): closest matches first, and among equally close ones the better-known games.

Firewatch
Shared: Adventure · Walking Simulator · Atmospheric

What Remains of Edith Finch
Shared: Walking Simulator · Atmospheric · Adventure

The Beginner's Guide
Shared: Indie · Walking Simulator · Short

Among the Sleep - Enhanced Edition
Shared: Indie · Horror · Adventure

Layers of Fear (2016)
Shared: Horror · Walking Simulator · Indie

Poppy Playtime
Shared: Horror · First-Person · Singleplayer

Outlast
Shared: Horror · First-Person · Atmospheric

Little Nightmares
Shared: Horror · Adventure · Atmospheric

Gone Home
Shared: Short · Indie · Walking Simulator

Amnesia: A Machine For Pigs
Shared: Horror · Walking Simulator · First-Person

From The Darkness
Shared: Indie · Horror · First-Person

Blair Witch
Shared: Adventure · Indie · Horror

The Room
Shared: Adventure · Indie · Atmospheric

Slender: The Arrival
Shared: Indie · Horror · First-Person

Little Nightmares II
Shared: Adventure · Horror · Atmospheric

Mouthwashing
Shared: Horror · Indie · Atmospheric

LIMBO
Shared: Indie · Adventure · Atmospheric

Iron Lung
Shared: Horror · Indie · Short

Scanner Sombre
Shared: Horror · Walking Simulator · Adventure

The Park®
Shared: Horror · Walking Simulator · First-Person

MiSide
Shared: Horror · First-Person · Atmospheric

No one lives under the lighthouse Director's cut
Shared: Indie · Adventure · Horror

Welcome to Kowloon
Shared: Horror · Adventure · Atmospheric

Visage
Shared: Horror · First-Person · Indie