Games like Ilamentia
Games like Ilamentia include Antichamber, The Witness, Manifold Garden, Outer Wilds, and The Talos Principle. We matched them by the tags players give Ilamentia on Steam (Puzzle, Indie, First-Person, Surreal, and Psychedelic): closest matches first, and among equally close ones the better-known games.

Antichamber
Shared: Puzzle · Indie · First-Person

The Witness
Shared: Puzzle · First-Person · Exploration

Manifold Garden
Shared: Puzzle · Surreal · First-Person

Outer Wilds
Shared: Exploration · Puzzle · Mystery

The Talos Principle
Shared: Puzzle · First-Person · Atmospheric

Viewfinder
Shared: Puzzle · First-Person · Surreal

NaissanceE
Shared: Indie · Exploration · First-Person

Superliminal
Shared: Puzzle · First-Person · Surreal

Hylics
Shared: Indie · Surreal · Psychedelic

Kairo
Shared: Puzzle · Indie · First-Person

Firewatch
Shared: First-Person · Atmospheric · Indie

Obduction
Shared: Puzzle · Indie · First-Person

What Remains of Edith Finch
Shared: First-Person · Atmospheric · Exploration

Return of the Obra Dinn
Shared: Puzzle · Indie · First-Person

Chants of Sennaar
Shared: Puzzle · Indie · Colorful

Blue Prince
Shared: Puzzle · Exploration · First-Person

The Beginner's Guide
Shared: Indie · First-Person · Atmospheric

INFRA
Shared: Puzzle · First-Person · Exploration

Call of the Sea
Shared: Puzzle · First-Person · Indie

Moncage
Shared: Puzzle · Indie · Surreal

OneShot
Shared: Indie · Puzzle · Atmospheric

Broken Reality
Shared: Indie · Surreal · Exploration

The Room
Shared: Puzzle · Indie · Atmospheric

The Unfinished Swan
Shared: Puzzle · Indie · Exploration