Games like RADARjAM
Games like RADARjAM include LUFTRAUSERS, Vampire Survivors, Jet Lancer, Planes, Bullets and Vodka, and BALL x PIT. We matched them by the tags players give RADARjAM on Steam (Flight, Bullet Hell, Shoot 'Em Up, Arcade, and 2D): closest matches first, and among equally close ones the better-known games.

LUFTRAUSERS
Shared: Bullet Hell · Arcade · Action

Vampire Survivors
Shared: Bullet Hell · 2D · Singleplayer

Jet Lancer
Shared: Flight · Action · Shoot 'Em Up

Planes, Bullets and Vodka
Shared: Shoot 'Em Up · Bullet Hell · Action

BALL x PIT
Shared: Bullet Hell · Arcade · Action

ZeroRanger
Shared: Shoot 'Em Up · Bullet Hell · Action

Bit Blaster XL
Shared: Bullet Hell · Shoot 'Em Up · Arcade

Super Hexagon
Shared: Arcade · Fast-Paced · Indie

Exit the Gungeon
Shared: Arcade · Bullet Hell · Action

Savant - Ascent
Shared: Action · Shoot 'Em Up · Bullet Hell

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

Ikaruga
Shared: Bullet Hell · Shoot 'Em Up · Arcade

Star Saviors
Shared: Bullet Hell · Shoot 'Em Up · Action

One Finger Death Punch
Shared: Action · Fast-Paced · Indie

Hotline Miami 2: Wrong Number
Shared: Action · Fast-Paced · Pixel Graphics

Hotline Miami
Shared: Action · Indie · Pixel Graphics

Nova Drift
Shared: Bullet Hell · Shoot 'Em Up · Arcade

Touhou Tenkuushou ~ Hidden Star in Four Seasons.
Shared: Bullet Hell · Shoot 'Em Up · Singleplayer

Timberman
Shared: 2D · Action · Arcade

Star of Providence
Shared: Bullet Hell · Shoot 'Em Up · Action

UBERMOSH:WRAITH
Shared: Arcade · Action · Bullet Hell

DRAINUS
Shared: Shoot 'Em Up · Action · Bullet Hell

Cyberhunt
Shared: Shoot 'Em Up · Action · Indie

Touhou Koumakyou: New Classic - the Embodiment of Scarlet Devil
Shared: Bullet Hell · Shoot 'Em Up · Action