Neat! Last I remembered of that, they were still experimenting with loading PiD maps into Forge. There's also a simplified spin on it for Doom 3:https://www.moddb.com/mods/pathways-redux/>>191239
By early, you mean before Myth & Oni? Not really.
Pathways is less of an FPS, more of an adventure game (conversation system, inventory puzzles, all levels are interconnected and you have to revisit locations on multiple occasions, etc.) built atop an FPS's combat/exploration engine. This mixed, slower pace is why I said something like it would be ideal for Receiver's cumbersome weapon mechanics (in addition to Pathways having an unusually detailed system for handling weapons, where bullets are tracked in individual mags that you move in and out of weapons similarly to a filebrowser)
and probable focus on VR.
Minotaur is supposedly (only one of these I didn't play) rather unique, a realtime tilebased PvP RPG. There was also a decent turnbased SP RPG based off it by a college buddy, Isles of Nemesis.
Marathon 1 is the most Id-like, somewhat similar to Doom, but (aside from the obvious technical advancements), has the story terminals giving more flavor (and map hints), some friendly monsters, movement-wise everything is floatier and more reliant on inertia, while combat-wise there is more of a focus on dodge-able projectiles versus Doom's tendency toward hitscan enemies, also a much bigger use of player teleportation than Doom. The latter two Marathon games also added liquids that could be swam in, and extensive use of monster/item teleportation, as well as a large focus on oxygen exhaustion due to vacuum levels and submersion.
Then there were a few Marathon-based licensed games, including a really good proto-Ghost Recon squad FPS called Damage Inc., a mediocre Duke Nukem-like FPS set in Washington D.C. called Prime Target, and an absolutely bizarre comicbook licensed game called Zero Population Count.Post too long. Click here to view the full text.