Games like Road Defense: Outsiders
Games like Road Defense: Outsiders include Vampire Survivors, Megabonk, 20 Minutes Till Dawn, Death Must Die, and Halls of Torment. We matched them by the tags players give Road Defense: Outsiders on Steam (Action Roguelike, Casual, Pixel Graphics, Top-Down Shooter, and Action): closest matches first, and among equally close ones the better-known games.

Vampire Survivors
Shared: Action Roguelike · Pixel Graphics · Roguelite

Megabonk
Shared: Action Roguelike · Roguelite · Action

20 Minutes Till Dawn
Shared: Action Roguelike · Top-Down Shooter · Roguelite

Death Must Die
Shared: Action Roguelike · Pixel Graphics · Roguelite

Halls of Torment
Shared: Action Roguelike · Pixel Graphics · Roguelite

BALL x PIT
Shared: Action · Action Roguelike · Roguelite

Nuclear Throne
Shared: Action Roguelike · Pixel Graphics · Action

Hades
Shared: Action Roguelike · Roguelite · Action

Rocket Rats
Shared: Action Roguelike · Pixel Graphics · Casual

Boneraiser Minions
Shared: Action Roguelike · Pixel Graphics · Roguelite

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

Goobies
Shared: Action Roguelike · Top-Down Shooter · Casual

Noobs Want to Live
Shared: Pixel Graphics · Action Roguelike · Action

Yet Another Zombie Survivors
Shared: Action Roguelike · Top-Down Shooter · Roguelite

Enter the Gungeon
Shared: Action Roguelike · Pixel Graphics · Bullet Hell

Brotato
Shared: Action Roguelike · Bullet Hell · Singleplayer

Soulstone Survivors
Shared: Action Roguelike · Roguelite · Bullet Hell

Hades II
Shared: Action · Action Roguelike · Roguelite

SYNTHETIK: Legion Rising
Shared: Top-Down Shooter · Action Roguelike · Action

Apocalypse Party
Shared: Casual · Action Roguelike · Top-Down Shooter

Deep Rock Galactic: Survivor
Shared: Action Roguelike · Top-Down Shooter · Roguelite

Blazing Beaks
Shared: Action Roguelike · Pixel Graphics · Top-Down Shooter

Asgard's Fall — Viking Survivors
Shared: Action Roguelike · Casual · Pixel Graphics

The Binding of Isaac: Rebirth
Shared: Action Roguelike · Pixel Graphics · Indie