Games like Slime Siege
Games like Slime Siege include Emberward, Element TD 2 - Tower Defense, Orcs Must Die! 3, Dungeon Defenders, and Age of Darkness: Final Stand. We matched them by the tags players give Slime Siege on Steam (Roguelite, Tower Defense, Indie, Strategy, and Real Time Tactics): closest matches first, and among equally close ones the better-known games.

Emberward
Shared: Tower Defense · Roguelite · Strategy

Element TD 2 - Tower Defense
Shared: Tower Defense · Real Time Tactics · Strategy

Orcs Must Die! 3
Shared: Tower Defense · Strategy · PvE

Dungeon Defenders
Shared: Tower Defense · Strategy · Character Customization

Age of Darkness: Final Stand
Shared: Tower Defense · Strategy · PvE

Artisan TD
Shared: Tower Defense · Strategy · Real Time Tactics

Rogue Tower
Shared: Tower Defense · Strategy · Roguelite

Thronefall
Shared: Tower Defense · Strategy · 3D

Bloons TD 6
Shared: Tower Defense · Strategy · 3D

Axon TD: Uprising - Tower Defense
Shared: Tower Defense · Roguelite · Real Time Tactics

Kingdom Rush - Tower Defense
Shared: Tower Defense · Strategy · Fantasy

Orcs Must Die! Deathtrap
Shared: Tower Defense · Roguelite · Strategy

The King is Watching
Shared: Tower Defense · Strategy · Roguelite

Sir, We Have an Orc Problem
Shared: Tower Defense · Roguelite · PvE

Yokai Art: Night Parade of One Hundred Demons
Shared: Roguelite · Tower Defense · Strategy

GemCraft - Chasing Shadows
Shared: Tower Defense · Indie · Strategy

Wall World
Shared: Roguelite · Tower Defense · Strategy

Shape of Dreams
Shared: Roguelite · PvE · Indie

Shadow Tactics: Blades of the Shogun
Shared: Strategy · Real Time Tactics · Indie

Inkbound
Shared: Roguelite · PvE · Strategy

Bills Must Be Paid
Shared: Roguelite · Strategy · Indie

XCOM 2
Shared: Strategy · Character Customization · Tactical

Bad North: Jotunn Edition
Shared: Tower Defense · Real Time Tactics · Indie

Total War: WARHAMMER III
Shared: Strategy · Real Time Tactics · Fantasy