For a game to be part of the list needs to:

• Be in a first-person perspective
  
• Be a 2.5D game (3D environment and sprites or 2D objects)
  
• Be a fast-paced shooter
  
• Have maps with verticality or depth on the Y axis (high and low places, stairs, elevators, etc.)

Have in mind that as more games are added, the requirements could change. Also, this list is SUBJECTIVE and might have exceptions.
If there is a game that should not be here or you think that a game can be a candidate to be here, please let me know in the comments.

A.W.O.L. (FREE)
Apocalyptic Vibes (Demo available)
Arthurian Legends (Demo available)
Autumn Night 3D Shooter
Beyond Citadel (Demo available)
Beyond Sunset (Demo and DLC available)
Blood: Fresh Supply™
Blood Refreshed Supply (Coming soon)
Borrowhelen (DLCs available)
Box Party (Coming soon) (Demo available)
Break
Brutal Fate (Coming soon)
Captain Wayne - Vacation Desperation (Coming soon) (Demo Available)
Caesar's Revenge
Chains of Fury (Coming soon)
Classic Marathon (FREE)
Classic Marathon 2 (FREE) (DLC available)
Classic Marathon Infinity (Coming soon) (FREE)
Cultic (Demo and DLC available)
CyClones*
Delilah (Coming soon)
DI: Debt is Inevitable (Coming soon)
Diluvian Ultra
Dismantled
Dismantled Director's Cut
Divine Frequency (Coming soon) (Demo available)
Duke Nukem 3D: 20th Anniversary World Tour
Enigmatic Worlds (Coming soon) (Demo available)
Eradicator
Fallen Aces
Fashion Police Squad (Demo and DLC available)
Final Absolution (Coming soon)
Fingerbang: All Bullets Pointin' (FREE)
Fish Person Shooter
Forgive Me Father
Forgive Me Father 2
Fortunes Run (DLC available)
Friendship Island
Fury's Sky (FREE)
Hands of Necromancy
Hands of Necromancy II
Haunted: Attack of the Dead Men (Coming soon) (Demo available)
Hedon Bloodrite (Includes Hedon I) (Demo and DLC available)
Hell Worlds Reinvigorated (Coming soon) (Demo available)
Hellgate Senigallia Remake
Hellslinger (Coming soon) (Demo available)
Heretic + Hexen
Horryefieing: High Rise
HYPERVIOLENT
I Am Sakuya: Touhou FPS Game (DLC available)
Impaler
Ion Fury (Previosly known as Ion Maiden) (DLCs available)
Killing Time
Killing Time: Resurrected
Last Rites
Liquidator (FREE)
Lycanthorn II - Rain of Beasts (Includes Lycanthorn I) (FREE)
M.E.A.T. II: Absolute Zero (Coming soon) (Demo available)
Mala Petaka (Demo available)
Mouse (Coming soon)
MULLET MAD JACK (Demo and DLCs available)
NAM
Nightmare Reaper (DLC available)
Oil Invasion
Old Retro Shooter
Only Lead Can Stop Them (Coming soon) (Demo available)
Outlaws + A Handful of Missions
PO'ed: Definitive Edition
Post Void
PowerSlave (DOS Classic Edition) (DLC available)
PowerSlave Exhumed
ProBoon Lite (Coming soon)
Prodeus (DLCs available)
Project Absentia (Demo and DLC available)

* Uses a modified Wolfenstein 3D engine

Project Warlock II
Randy Blaster 3D (FREE) (DLC available)
Realms of the Haunting
Redneck Deer Huntin'
Redneck Rampage
Redneck Rampage Rides Again
Redneck Rampage: Possum Bayou (Coming soon) (Extended demo)
REKKR: Sunken Land
Relentless Frontier (Demo available)
Retroninjacyberassassin (FREE) (DLCs available)
Rise of the Triad: Dark War
Rise of the Triad: Ludicrous Edition (Includes Return to the Triad) (Demo available)
Rogue Shooter: The FPS Roguelike (Demo available)
Rule No. 1 (DLC available)
Rule No. 2
RUSSIA BATTLEGROUNDS
Selaco
Shadow Warrior Classic (1997) (FREE)
Shadow Warrior Classic Redux
SharpShooter3D (DLC available)
Shrine (FREE)
Shrine II (FREE)
SKELET_666 (Coming soon) (Demo available)
Slayers X: Terminal Aftermath: Vengance of the Slayer (Demo and DLC available)
Snap the Sentinel (Coming soon) (Demo available)
STAR WARS™- Dark Forces
STAR WARS™: Dark Forces Remaster
Stellar Valkyrie (Coming soon)
Strife: Veteran Edition
SUFFER (DLC available)
SUFFER 2 (DLC available)
Supplice (Demo available)
Terrorform
The Age of Hell (Coming soon) (Demo available)
The Apogee Throwback Pack
The Citadel (Demo available)
This Strange Realm of Mine (DLC available)
Twilight Manor: Roguelite FPS
Twilight Town: A Cyberpunk FPS
Unhinged 2 (Coming soon) (Demo available)
Viscerafest
Vomitoreum
Wanted 3D: Dead or Alive (Coming soon) (Demo available)
WARAG (Coming soon) (Demo available)
Warhammer 40,000: Boltgun
Warhammer 40,000: Boltgun 2 (Coming soon)
Wholesome Slaughter (DLC available)
Witchaven
Witchaven II: Blood Vengeance
World War II GI/WWII GI
Z.A.R.

Blood: One Unit Whole Blood
Duke Nukem 3D
Duke Nukem 3D: Megaton Edition
Electric Highways
Heretic: Shadow of the Serpent Riders
HeXen: Beyond Heretic
HeXen: Deathkings of the Dark Citadel
Shadow Warrior (Classic)
The Forgotten Sprites

Let me know if I'm missing something!

Looking for more lists like this one? check these game engine lists made by Wiggy and I:
List of Build Engine games
List of Doom Engine games on the Steam store
List of GoldSrc Games
List of Id Tech 2 games
List of Id Tech III games
List of Id Tech 4 games
List of Lithtech games
List of Quake 1 clones on the Steam store
List of Unreal Engine 1 games
List of Unreal Engine 2 games
List of Unreal Engine 3 games on the Steam store
List of Wolf 3D Engine games on the Steam store
List of Wolf 3D clones on the Steam store