The fact that the only person to finish your scenario frequently mentions that he cheated in order to get through the game should have been a HUGE clue to you that you needed to go back and redo some aspects of your design.
I only played through 1.25 of the levels before I quit.
Kudos for making a scenario at all; that's no small feat. Also, I liked your set pieces (such as the stasis pods, or whatever they were) which make it feel more like a "real" space we're playing in. Your terminals also looked really good.
This scenario is not difficult; it is a tedious waste of time. If it was difficult then I'd have to actually put effort into playing it.
Withholding save terminals (I didn't see any) does not make your scenario more difficult.
Starting the player at 1/4 health and withholding rechargers and canisters (I did not see any) does not make your scenario more difficult.
Giving the player an assault rifle but only two extra grenade packs (I didn't see any other ammo) does not make your game more difficult.
Hiding switches and doors that are mandatory to progress through a level does not make your game more difficult.
None of these things makes the game hard, it just makes the game arbitrarily unfair.
I quit after the third time I died (on Normal). Why would I waste time replaying everything from the start again? It's just switch hunting, backtracking, and the little combat that exists isn't fun.
Maybe the later levels are more fun and interesting, but you certainly don't seem to want me to get to them and find out.
9 levels. This may be the most difficult scenario you will ever play.
Here's a review from the only person I know that completed it.
I just finished Ra'thor (except for the hidden level, which I did not find the entry point for).
"I've been playing Marathon since late '95, and think I'm a pretty good player, but your scenario is hands down the most difficult I've ever played. In fact, I'd say it's pretty near impossible to beat on Total Carnage, especially the last 3 vacuum levels. I freely admit that I cheated constantly for oxygen and once or twice for ammo (especially on Igor Ra'thor), and occasionally used Forge. I do have a life, and I just didn't have the time (or desire) to play those levels over and over again to reach the level of perfection needed to complete them on the available oxygen or ammo (at least what I could find). I believe I never cheated for shields, but I may be mistaken. It took me a long time to get through the maps, so memory fades. You made free use of hidden switches that made things that much harder".
D. Supanich, North Hollywood, CA (March 2003)