Games like UnSeen
Games like UnSeen include Firewatch, What Remains of Edith Finch, Outer Wilds, The Room 4: Old Sins, and Amnesia: A Machine For Pigs. We matched them by the tags players give UnSeen on Steam (Horror, Exploration, Lovecraftian, Mystery, and Atmospheric): closest matches first, and among equally close ones the better-known games.

Firewatch
Shared: Atmospheric · Adventure · Mystery

What Remains of Edith Finch
Shared: Atmospheric · Mystery · Exploration

Outer Wilds
Shared: Exploration · Mystery · Adventure

The Room 4: Old Sins
Shared: Mystery · Lovecraftian · Adventure

Amnesia: A Machine For Pigs
Shared: Horror · Atmospheric · Exploration

DREDGE
Shared: Exploration · Lovecraftian · Adventure

SOMA
Shared: Horror · Atmospheric · Exploration

The Vanishing of Ethan Carter
Shared: Mystery · Exploration · Atmospheric

Layers of Fear (2016)
Shared: Horror · Atmospheric · Story Rich

The Room Two
Shared: Mystery · Horror · Atmospheric

CARIMARA: Beneath the forlorn limbs
Shared: Exploration · Mystery · Horror

Still Wakes the Deep
Shared: Horror · Lovecraftian · Story Rich

The Painscreek Killings
Shared: Exploration · Mystery · Horror

The Room Three
Shared: Mystery · Adventure · Atmospheric

Blue Prince
Shared: Exploration · Mystery · Story Rich

The Room
Shared: Mystery · Atmospheric · Adventure

Dagon: by H. P. Lovecraft
Shared: Horror · Lovecraftian · Atmospheric

INFRA
Shared: Exploration · Atmospheric · Mystery

Call of the Sea
Shared: Adventure · Lovecraftian · Story Rich

Call of Cthulhu®
Shared: Horror · Lovecraftian · Atmospheric

Amnesia: Rebirth
Shared: Horror · Exploration · Story Rich

The Forgotten City
Shared: Exploration · Mystery · Adventure

SUNLESS SEA
Shared: Exploration · Lovecraftian · Story Rich

Quern - Undying Thoughts
Shared: Mystery · Exploration · Adventure