Games like In a Barrel
Games like In a Barrel include Vampire Survivors, LUFTRAUSERS, Exit the Gungeon, Windowkill, and BALL x PIT. We matched them by the tags players give In a Barrel on Steam (Action, Arcade, Bullet Hell, 2D, and Singleplayer): closest matches first, and among equally close ones the better-known games.

Vampire Survivors
Shared: Bullet Hell · 2D · Indie

LUFTRAUSERS
Shared: Arcade · Bullet Hell · Action

Exit the Gungeon
Shared: Arcade · Action · Bullet Hell

Windowkill
Shared: Action · Bullet Hell · Arcade

BALL x PIT
Shared: Action · Arcade · Bullet Hell

A Dance of Fire and Ice
Shared: Singleplayer · Arcade · 2D

Megabonk
Shared: Bullet Hell · Action · Indie

Rogue Legacy 2
Shared: Arcade · Action · Indie

Skul: The Hero Slayer
Shared: Action · Indie · 2D

Streets of Rage 4
Shared: Action · 2D · Arcade

Star Saviors
Shared: Action · Bullet Hell · Arcade

Timberman
Shared: Action · Indie · 2D

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

Boneraiser Minions
Shared: Bullet Hell · 2D · Indie

Halls of Torment
Shared: Bullet Hell · Action · Arcade

One Finger Death Punch
Shared: Action · Indie · Singleplayer

Just Shapes & Beats
Shared: Bullet Hell · Action · 2D

Touhou Fuujinroku ~ Mountain of Faith.
Shared: Action · Bullet Hell · Indie

Rogue Legacy
Shared: Action · Indie · Singleplayer

ZeroRanger
Shared: Bullet Hell · Action · Indie

DRAINUS
Shared: Action · Indie · Singleplayer

Revolution Ace
Shared: Action · Bullet Hell · Indie

Bit Blaster XL
Shared: Bullet Hell · Arcade · Action

Super Hexagon
Shared: Arcade · Indie · Action