Games like Red Horizon
Games like Red Horizon include Vampire Survivors, Planes, Bullets and Vodka, Timberman, Megabonk, and Bit Blaster XL. We matched them by the tags players give Red Horizon on Steam (Indie, Casual, Action, Free to Play, and Bullet Hell): closest matches first, and among equally close ones the better-known games.

Vampire Survivors
Shared: Bullet Hell · Indie · Pixel Graphics

Planes, Bullets and Vodka
Shared: Casual · Action · Bullet Hell

Timberman
Shared: Casual · Indie · Action

Megabonk
Shared: Indie · Bullet Hell · Action

Bit Blaster XL
Shared: Bullet Hell · Action · Difficult

LUFTRAUSERS
Shared: Indie · Action · Bullet Hell

Cyberhunt
Shared: Indie · Casual · Action

Exit the Gungeon
Shared: Indie · Action · Bullet Hell

Enter the Gungeon
Shared: Bullet Hell · Indie · Pixel Graphics

UFO 50
Shared: Indie · Action · Pixel Graphics

Hotline Miami
Shared: Indie · Action · Pixel Graphics

Shovel Knight: Treasure Trove
Shared: Indie · Pixel Graphics · Retro

Skul: The Hero Slayer
Shared: Indie · Action · Pixel Graphics

ZeroRanger
Shared: Indie · Action · Bullet Hell

Trip to Vinelands
Shared: Indie · Action · Casual

Return.
Shared: Indie · Casual · Free to Play

Hotline Miami 2: Wrong Number
Shared: Action · Pixel Graphics · Indie

Broforce
Shared: Action · Pixel Graphics · Indie

Ultimate Custom Night
Shared: Free to Play · Difficult · Indie

Devil Daggers
Shared: Indie · Action · Difficult

Nuclear Throne
Shared: Indie · Pixel Graphics · Action

UBERMOSH Vol.5
Shared: Indie · Action · Pixel Graphics

Super Meat Boy
Shared: Indie · Difficult · Pixel Graphics

20 Minutes Till Dawn
Shared: Bullet Hell · Pixel Graphics · Casual