Project IYO

Descent came out really early in 1995. It was still all Doom back then...our feet was firmly on the ground :-)

There were of course space sims but even there you had no real feeling that you have 6 degrees of freedom because you were basically surrounded by nothing....space.

Descent 1 devs came along said....hmm, let's build a simulator but you get to play WITHIN the confines of closed spaces. Let's make maps that utilize this 6 degree of freedom and since now we were not in space the player could really appreciate that sometimes the floor is the ceiling. You entered a vertical shaft and suddenly the walls were the floor etc.

The game had such an impact (and was still financially not so successful) that to this day there are still people around trying to bring the essence of the original back. Forsaken, Miner Wars, Descent 3, Sublevel Zero (roguelite) and a huge project called Desecrators on Steam now. 

Meanwhile people from the original Parallax Crew are working on Ships That Fight Underground (STFU!). 

As for changes...you need a solid first person view. Third person reveals too much and takes away from the mind-bending aspect of the experience. 

You need levels that thrive on the 6 degrees. I think  I have seen smaller projects where you piloted a spaceship and you flew from room to room but the you always had the floor beneath you and the ceiling above you. The player just could have just walked. No good.

Weapons: yes you are inside mines (great choice by the original Devs) but you are still flying a modified spaceship. Descent was fairly straightforward with its lasers but later Descent-likes introduced rockets that upon explosion created a gravity field, pulling nearby enemies there, or missiles with cameras so you could guide it to your target just around the corner. Drones with cameras, drones who would help you find keys or even more. 

The color palette: many Descent clones play extremely well (Forsaken, Overload) but - and I know this is a technical issue - everything looks the same. Descent 1 used a very wide range of colors, you had no problem identifying what you were fighting. Compare System Shock 1 original to the remake. I'm either watching a neon show at times or I'm stuck because everything is the same color or shade of color...can't tell if I'm facing a wall, a door, or something else. 

Well, sorry for the long post but I hope I was helpful. Strictly my two cents as somebody who grew up during the 90s. 

PS: I really like Project THF and that you grasped one the greatest strength of the game...the non-linear level design. Been a while since I played it, hope you won't abandon the game. 

Kind Regards

Peter from Hungary