Oh, I love me some boomshoots. Doom, DUSK, Blood, Ion Fury, Shadow Warrior, Wizordum, Amid Evil and Duke Nukem have all been mentioned already and all of which are killer games. Amid Evil and Ion Fury also have expansion packs/DLC that are pretty sweet too. For instance, Amid Evil: The Black Labyrinth's melee weapon is a pair of magic gauntlets that make your fists into the Fists of the North Star, which is sweet. Ion Fury: Aftershock has pilotable jet skis with guns attached to them, which is also sweet. At this point there are so many good retro FPS games it's kinda crazy. Never thought as many of the fever dream concepts for games I came up when I was a little kid like Paperhead would be brought into reality.
Oh, and there is also Quake, which has some particularly dope mods like Arcane Dimensions or Alkaline that are basically Quake sequels we never got. Seriously, those mods are that high quality. Further into mods, there's stuff like Ashes 2063 and Reds Over World for Doom that are TCs that turn it into their own unique flavors of boomshoot. Plenty of excellent mods for Blood and Duke Nukem 3D too, like Death Wish or Alien Armageddon.
"Unless it has PS1 style graphics, I'll play nearly anything with that."
Check out Lunacid:
The King's Field inspired game that's honestly better than King's Field
That's a really good retro themed game, but honestly it's about as far from a Boomer Shooter as you could get.
The new Starship troopers FPS look lit very 90s.
Yes, it does. They even got FMV cutscenes with Casper Van Diem, which is amazing: