Games like Opalescence
Games like Opalescence include BALL x PIT, Vampire Survivors, Bit Blaster XL, Hotline Miami, and Planes, Bullets and Vodka. We matched them by the tags players give Opalescence on Steam (Action, Arcade, Top-Down Shooter, Colorful, and Bullet Hell): closest matches first, and among equally close ones the better-known games.

BALL x PIT
Shared: Action · Arcade · Bullet Hell

Vampire Survivors
Shared: Bullet Hell · 2D · Arcade

Bit Blaster XL
Shared: Bullet Hell · Arcade · Action

Hotline Miami
Shared: Action · Pixel Graphics · Top-Down

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

LUFTRAUSERS
Shared: Arcade · Action · Bullet Hell

Hotline Miami 2: Wrong Number
Shared: Action · Pixel Graphics · Top-Down Shooter

Exit the Gungeon
Shared: Arcade · Action · Bullet Hell

Sky Force Reloaded
Shared: Arcade · Top-Down Shooter · Bullet Hell

Broforce
Shared: Action · 2D · Pixel Graphics

UBERMOSH Vol.5
Shared: Action · Arcade · Bullet Hell

DoDonPachi Resurrection
Shared: Top-Down Shooter · Arcade · Bullet Hell

UBERMOSH Vol.3
Shared: Action · Arcade · Bullet Hell

UBERMOSH
Shared: Action · Arcade · Pixel Graphics

Nuclear Throne
Shared: Action · Bullet Hell · Top-Down Shooter

Angel at Dusk
Shared: Action · Bullet Hell · Shooter

Nova Drift
Shared: Arcade · Bullet Hell · Action

ESCHATOS
Shared: Top-Down Shooter · Bullet Hell · Arcade

Halls of Torment
Shared: Bullet Hell · Action · Arcade

ZeroRanger
Shared: Action · Bullet Hell · Arcade

Halo: Spartan Assault
Shared: Action · Top-Down Shooter · Shooter

Zombieville USA 3D
Shared: Action · Arcade · Top-Down Shooter

Rocket Rats
Shared: Bullet Hell · Action · 2D

Chippy
Shared: Bullet Hell · Top-Down Shooter · Arcade