Games like Firewall
Games like Firewall include HELLDIVERS™ 2, Squirrel with a Gun, Aimlabs, Hitman: Absolution, and Grand Theft Auto V Legacy. We matched them by the tags players give Firewall on Steam (3D Platformer, Shoot 'Em Up, Third-Person Shooter, Robots, and Stealth): closest matches first, and among equally close ones the better-known games.

HELLDIVERS™ 2
Shared: Third-Person Shooter · PvE · Shooter

Squirrel with a Gun
Shared: Third-Person Shooter · 3D Platformer · Platformer

Aimlabs
Shared: Third-Person Shooter · Shooter · First-Person

Hitman: Absolution
Shared: Stealth · Third-Person Shooter · Action

Grand Theft Auto V Legacy
Shared: Action · Third-Person Shooter · Shooter

Warhammer 40,000: Space Marine 2
Shared: Third-Person Shooter · PvE · Action

PUBG: BATTLEGROUNDS
Shared: Third-Person Shooter · Shooter · Action

ARC Raiders
Shared: Third-Person Shooter · PvE · Shooter

Tom Clancy’s Splinter Cell Blacklist
Shared: Stealth · Third-Person Shooter · Action

Akimbot
Shared: 3D Platformer · Third-Person Shooter · Platformer

The Callisto Protocol™
Shared: Third-Person Shooter · Shooter · PvE

007 First Light
Shared: Third-Person Shooter · Stealth · Shooter

STAR WARS™ Battlefront™ II
Shared: Third-Person Shooter · Shooter · Action

Tom Clancy's Ghost Recon® Wildlands
Shared: Shooter · Stealth · Third-Person Shooter

Ratchet & Clank: Rift Apart
Shared: 3D Platformer · Third-Person Shooter · Platformer

EARTH DEFENSE FORCE 6
Shared: Third-Person Shooter · Shooter · PvE

PRAGMATA
Shared: Third-Person Shooter · Robots · Action

Five Nights at Freddy's: Security Breach
Shared: Robots · Stealth · First-Person

Neon White
Shared: 3D Platformer · Platformer · Shooter

Tom Clancy's Ghost Recon: Future Soldier™
Shared: Third-Person Shooter · Stealth · Action

Warframe
Shared: Third-Person Shooter · Action · PvE

HITMAN World of Assassination
Shared: Stealth · Third-Person Shooter · Action

Portal 2
Shared: Platformer · 3D Platformer · First-Person

Mafia: The Old Country
Shared: Third-Person Shooter · Stealth · Action