Games like Half-Life Deathmatch: Source
Games like Half-Life Deathmatch: Source include Black Mesa, DOOM, Half-Life 2, DOOM Eternal, and Half-Life. We matched them by the tags players give Half-Life Deathmatch: Source on Steam (Action, FPS, Multiplayer, Shooter, and Sci-fi): closest matches first, and among equally close ones the better-known games.

Black Mesa
Shared: FPS · Action · Sci-fi

DOOM
Shared: FPS · Action · Shooter

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

DOOM Eternal
Shared: FPS · Action · Shooter

Half-Life
Shared: FPS · Sci-fi · Multiplayer

Call of Duty®
Shared: FPS · Multiplayer · Action

Halo Infinite
Shared: FPS · Multiplayer · Action

Counter-Strike
Shared: Action · FPS · Multiplayer

Call of Duty®: Black Ops III
Shared: Multiplayer · FPS · Action

Halo: The Master Chief Collection
Shared: FPS · Multiplayer · Classic

Titanfall® 2
Shared: FPS · Multiplayer · Shooter

Apex Legends™
Shared: Multiplayer · FPS · Shooter

STAR WARS™ Battlefront II (Classic, 2005)
Shared: Action · Multiplayer · Shooter

PUBG: BATTLEGROUNDS
Shared: Shooter · Multiplayer · FPS

BioShock Infinite
Shared: Action · FPS · Shooter

Counter-Strike: Condition Zero
Shared: Action · FPS · Multiplayer

Battlefield™ 1
Shared: FPS · Multiplayer · Action

Counter-Strike: Source
Shared: FPS · Action · Shooter

Ready or Not
Shared: FPS · Shooter · Multiplayer

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

Left 4 Dead 2
Shared: FPS · Multiplayer · Action

STAR WARS™ Republic Commando™
Shared: Action · FPS · Sci-fi

Battlefield™ 2042
Shared: FPS · Multiplayer · Shooter

Quake
Shared: FPS · Action · Shooter