>>3662868
Wolfenstein: grid-based levels, no elevation, no light levels.
Doom: non-grid levels (rooms of any shape), elevation and elevators as well as deep pits and crushers, textured floors and ceilings, varying light levels and light effects (blinking lights). Still no looking up/down.
Rise of the Triad: Same as Wolf, but with elevations and ability to jump via jump pads.
Heretic: Same as Doom, but inventory system is introduced, as well as ability to fly, and special weapon properties like some weapons passing through ghost monsters. Can look up and down a bit in a hacky way.
System Shock - not really FPS, yet still a first person game: Grid based levels, but has slopes (which Doom does not), and triangular grid elements that allow for more varied room shapes (like 8-sided room) than wolf, elevation and light levels. Also jumps. Robust inventory and RPG systems.
Wichaven: Build game, slopes, light levels, breakable weapons and inventory system, very limited room-over room. Ability to jump, crouch, look up and down, climb ladders.
Hexen: same as Heretic, but hubs and scripts that affect other sub-levels in a hub you currently in. Ability to jump.
Duke: Build game, has slopes, viewportals, room over room with some limitations, better at looking up/down but still hacky and limited. Scripted destructible environment and non-euclidean space possible with use of portalling.
PSX Doom: colored lighting.
Witchaven 2: Duke+Witchaven, with ability to make your own ladder out of arrows.
Blood: Same as Duke, but voxel objects.
Shadow Warrior: same as Duke+Blood, ability to delegate inputs to other objects (RC cars, driveable vehicles, limited).
Quake: true 3D.
Haven't played Marathon so can't tell where it fits in the progression list.