Games like Exostorm
Games like Exostorm include LUFTRAUSERS, ZeroRanger, BALL x PIT, Touhou Fuujinroku ~ Mountain of Faith., and Touhou Koumakyou: New Classic - the Embodiment of Scarlet Devil. We matched them by the tags players give Exostorm on Steam (Action, Indie, Bullet Hell, and Shoot 'Em Up): closest matches first, and among equally close ones the better-known games.

LUFTRAUSERS
Shared: Indie · Bullet Hell · Action

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

BALL x PIT
Shared: Action · Bullet Hell · Shoot 'Em Up

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

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

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

Revolution Ace
Shared: Action · Indie · Shoot 'Em Up

TouHou Makuka Sai ~ Fantastic Danmaku Festival Part II
Shared: Indie · Bullet Hell · Shoot 'Em Up

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

Vampire Survivors
Shared: Bullet Hell · Indie · Action

The Void Rains Upon Her Heart
Shared: Bullet Hell · Indie · Action

Savant - Ascent
Shared: Action · Indie · Shoot 'Em Up

TouHou Makuka Sai ~ Fantastic Danmaku Festival
Shared: Indie · Action · Bullet Hell

Touhou Kouryudou ~ Unconnected Marketeers.
Shared: Action · Bullet Hell · Shoot 'Em Up

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

Jets'n'Guns 2
Shared: Action · Indie · Shoot 'Em Up

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

Sky Force Reloaded
Shared: Shoot 'Em Up · Bullet Hell · Action

Megabonk
Shared: Indie · Bullet Hell · Action

Touhou Blooming Chaos 2
Shared: Action · Indie · Bullet Hell

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

BLUE REVOLVER
Shared: Indie · Bullet Hell · Action

Maiden and Spell
Shared: Action · Indie · Bullet Hell

Touhou Juuouen 〜 Unfinished Dream of All Living Ghost.
Shared: Action · Bullet Hell · Shoot 'Em Up