Games like The Spooky Island
Games like The Spooky Island include Firewatch, Layers of Fear (2016), Little Nightmares, Mouthwashing, and From The Darkness. We matched them by the tags players give The Spooky Island on Steam (Linear, Indie, Horror, Adventure, and Walking Simulator): closest matches first, and among equally close ones the better-known games.

Firewatch
Shared: Adventure · Walking Simulator · Atmospheric

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

Little Nightmares
Shared: Horror · Adventure · Indie

Mouthwashing
Shared: Horror · Indie · Psychological Horror

From The Darkness
Shared: Horror · Indie · Dark

Sally Face - Episode One
Shared: Indie · Horror · Dark

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

Little Nightmares II
Shared: Horror · Adventure · Dark

Poppy Playtime
Shared: Horror · Dark · Indie

Visage
Shared: Horror · Dark · Psychological Horror

Psalm 5:9-13
Shared: Indie · Horror · Walking Simulator

SOMA
Shared: Horror · Atmospheric · Psychological Horror

Amnesia: A Machine For Pigs
Shared: Horror · Walking Simulator · Atmospheric

Blair Witch
Shared: Horror · Indie · Adventure

Welcome to Kowloon
Shared: Horror · Adventure · Walking Simulator

Outlast
Shared: Horror · Atmospheric · Psychological Horror

9 Childs Street
Shared: Indie · Horror · Dark

Scanner Sombre
Shared: Horror · Walking Simulator · Adventure

Bad Parenting 1: Mr. Red Face
Shared: Horror · Adventure · Walking Simulator

No, I'm not a Human
Shared: Horror · Indie · Psychological Horror

Layers of Fear 2 (2019)
Shared: Indie · Horror · Walking Simulator

Darkwood
Shared: Horror · Adventure · Dark

DISTRAINT: Deluxe Edition
Shared: Indie · Horror · Adventure

Hellblade: Senua's Sacrifice
Shared: Atmospheric · Adventure · Horror