Games like Alien Earth
Games like Alien Earth include Half-Life 2, Halo: Spartan Assault, Crysis Remastered, Aliens: Dark Descent, and Black Mesa. We matched them by the tags players give Alien Earth on Steam (Action, Adventure, Strategy, Isometric, and Sci-fi): closest matches first, and among equally close ones the better-known games.

Half-Life 2
Shared: Action · Sci-fi · Adventure

Halo: Spartan Assault
Shared: Action · Sci-fi · Strategy

Crysis Remastered
Shared: Action · Sci-fi · Aliens

Aliens: Dark Descent
Shared: Action · Strategy · Sci-fi

Black Mesa
Shared: Action · Sci-fi · Atmospheric

Halo: Spartan Strike
Shared: Action · Sci-fi · Strategy

The Bureau: XCOM Declassified
Shared: Action · Sci-fi · Strategy

Half-Life: Opposing Force
Shared: Action · Sci-fi · Adventure

Half-Life: Blue Shift
Shared: Action · Sci-fi · Aliens

Shadow Tactics: Aiko's Choice
Shared: Strategy · Action · Isometric

Defense Grid: The Awakening
Shared: Strategy · Sci-fi · Aliens

PRAGMATA
Shared: Action · Sci-fi · Adventure

XCOM®: Chimera Squad
Shared: Strategy · Sci-fi · Aliens

Crysis 2 - Maximum Edition
Shared: Action · Sci-fi · Aliens

Dead Space (2008)
Shared: Action · Sci-fi · Atmospheric

Alien: Isolation
Shared: Sci-fi · Atmospheric · Aliens

BioShock Infinite
Shared: Action · Adventure · Atmospheric

X-Morph: Defense
Shared: Action · Strategy · Sci-fi

Aliens vs. Predator™
Shared: Action · Sci-fi · Aliens

STAR WARS Jedi: Survivor™
Shared: Action · Adventure · Sci-fi

Warhammer 40,000: Space Marine 2
Shared: Action · Adventure · Sci-fi

Deliver Us The Moon
Shared: Adventure · Action · Sci-fi

Natural Selection 2
Shared: Strategy · Action · Sci-fi

Homeworld: Deserts of Kharak
Shared: Strategy · Sci-fi · Action