I've tried writing this post a couple of times and I want to make sure that I get it right because my goal here is not to discourage you or make you stop working on this. I had very little familiarity with Dead Marine before I played this version, and my initial impression was that Redux felt like a Vanilla+/Vanilla Enhancement mod with a bunch of random stuff thrown in. Playing the original version after playing this, it turns out that's exactly the case.
I think most of my problems stem from the fact that the original Dead Marine indeed was a vanilla enhancement mod with a pretty solid goal. Just going by Gifty's original ReadMe.txt (still included in the PK3):
Dead Marine is a weapons/gore/HUD/general enhancement mod which aims to make Doom moodier, make the combat punchier, and generally spice up the game without changing any of the gameplay or mechanics. All additions are meant to be "lore-friendly" and look as close to Id's original style as possible.
Which in general just goes against almost everything added in this Redux version. I think what you're doing
could work if there was more consideration put into these additions, but a majority of the things I've seen you add have been independently made by someone else. I know some of this stuff doesn't require permission to be used, but it seems a bit suspect that all of the additions are things that have been released on the resource sub-forum or Realm667. I think what made me raise an eyebrow the most is the addition of DarkDoomZ, which is still actively being worked on and could ideally just be loaded as a separate PK3. There is also an issue that (I believe) has present ever since it was been added which is the weapon sway cutting off weapon sprites when looking up and down. I'm not entirely sure why something like that would be implemented if it's been broken since day one, and nothing about the sprites were changed to compensate for it. Normally what I would recommend is adjusting the code to not push the sprite up so far, but I don't think that's a viable option considering the following...
It looks like everything you've added has just been thrown into the root directory of the PK3. It would explain the host of errors when starting the game because this is an absolute mess internally. You have 28 files just named
"DECORATE", 14 named
"ZScript", two
KEYCONFs, and a ton of other random credit files from the original WADs and PK3s you copied the content from. If this was something you made from scratch, I'd totally understand, but you started with a really good base in Dead Marine, which has more than enough examples of clean, proper file structure. The DECORATE file that was originally in Dead Marine even shows you how Gifty used
#include, an extremely helpful directive to remove clutter and make it easier for you to find errors. Almost all of these could be consolidated into independently named files, and again I have to stress that this is mostly beneficial to YOU because without it, all GZDoom is going to show you is that there is an error in a file named DECORATE on line 123 and you're going to have to search through the 28 files named DECORATE in order to figure out what's wrong. I think you should really take some time to understand how these files work rather than throwing them into your mod, it'd be a really good learning experience and it'd help you learn how everything works better.
Outside of that, the gameplay is also really unpolished. The new weapon additions (rifle, grenade especially) feel so lifeless compared to the weaponry that came from Dead Marine. I'm not entirely sure I've ever heard of anyone positively describing enemies as "bullet-spongey". It's artificial difficulty. An enemy being hard to kill because of how they're used, placed on a map, or their unique attacks are ALWAYS going to be more fun than an enemy who is hard to kill because there's an extra zero added to its health. I have no problem with enemies being hard to deal with or gameplay being difficult, but here I don't think there is enough consideration and understanding to make it fun and engaging for the player. The enemy roster feels very misplaced and misused because of this, with Archvile replacements being extremely easy to kill and the Spider Mastermind being just straight up the Hell Knight from the very very recently released
Legion of Bones (which come on, it hasn't even been out for a month and you're just straight up using it wholesale). Not to mention removing saving is a huge misstep for a gameplay mod that doesn't include levels. Are you expecting a Soulsphere on every map? What about situations where you need +100 health and instead of a Soulsphere before a fight, you get a save? That seems like a glaring error to me.
All in all, I want to stress that I
think I can see what you're trying to do with this, but I think you need to go back to the basics and try working on something of your own first. Making something from the ground up is going to give you a better understanding of Doom and its gameplay, it'll help you tailor extra additions better, and you'll learn
a ton along the way. It's clear you're wanting to do something vastly different from Dead Marine anyways, perhaps making your own brand new weapons and enemies will help you accomplish what you're aiming for. As it stands right now, I don't think you're going to be learning much when you're just copying and pasting wads and PK3s into your own mod without understanding how any of it truly works.