A total ramble about Doom and Doom Eternal haha, have fun:
difference D;E and D2016
Doom was about freedom and mobility in combat, but had the problem of not really starring the main combat mainstay i.e. status-changes. You couldn't really sweep enemies, knock them down or anything, you either had them be alive, or dead.
This saw Doom become a numbers game really fast. You see a foe and you look at how you can kill it the most efficient. And this can go two routes, you can go the path of least resistance or the path of optimal gameplay.
Least resistance would be in that game to just equip the supershotgun and run at enemies nuking them with its high damage and ammo capacity. Not optimal, but requires the least inputs and effort from the player while also being rewarded with up close gore and a good SFX from the shotty.
The other being an optimal combo (SS, Gaus, RPG) to kill enemies as fast as possible, with some foes having different combos that are faster.
The later is interesting since there's a few things added into that like fuel-management, allowing players that plan ahead to either get a lot of ammo refills by chainsawing a lot of smaller enemies, or quickly take care of a big menace, offering some freedom in combat. Other options include a decoy to free up some space etc. Giving he player some form of playerfreedom.
It also had some unique shooter elements like a DoT in the form of remote detonation, which is quite novel for shooters outside of flamethrowers.
In Doom Eternal, the devs saw people play in both of these ways and made a concious decision which one was preferable, namely a take on the second version (weapon switching).
Instead of looking at what made the style they didn't want to appear, appear, they focused on forcing players into that second style. Player is constantly using the same weapon and not switching to others or using the chainsaw to replenish ammo or glorykills to heal? Slice the ammo-capacity into a quarter of its original state, now he has to.
Not chainsawing enough? The original pip now also regenerates constantly and ammo pickups are less. Either you chainsaw or you die.
No glorykills? Enemies deal buckets more damage and healing-pickups are less frequent. Glory or die.
The result is players running against a wall since their original style doesn't work, and so they either stop or adopt the "correct" style of play.
THe downside here is that veteran players now have less freedom as a result. A lot of the more mechanical toys have been removed in favour of cooldowns (easier to manage), a lot of subweapons are similar (shockwave explosion), some toys have been removed (decoy grenade) and the fuel-management is now gone to force a playstyle they were doing anyway.
So in a sense the skill floor has been lowered in a sense, as you're absolutely forced into that playstyle. But the skill ceiling has also been lowered as a consequence, with the only freedom coming from "might as well use bad options to mix it up".
You can see attempts to fix problems with having enemies have removable limbs, but generally speaking these don't offer the state-change that is necessary to overrule "just kill them" as an option. Removing limbs deals monsterous damage, so it is also the prefered damage option most of the time. It is rarely a better choice to "delimb the gun of all foes and then kill them" over "just kill them fast", especially due to the high damage output enemies have.
Another problem that totally went unfixed as well was weapon variety. One big problem was players, in their numbers game, sticking to either one or three weapons. And this has a lot to do with the overlap the weapons have.
Let's take D:E as an example.
We have two machine guns that share ammo, with one also having a sniper function and homing missile function: all sharing the same ammo group. We then have a nuke and a projectile based machine gun that share ammo, a rocket, two shotguns and three super weapons, one being an OHKO, the other a high damage multitarget weapon, the latter a high damage single target weapon.
There is no reason other than "we had these weapons before" and aesthetic reasons that the HMG and Gattling gun cannot be combined, or that the Gattling gun isn't a mod for the HMG (or just a plain secondary fire). The Sniper can share this as well.
Seeker Missiles can be relegated to the RPG, giving it a high single target attack( regular shot) and a low damage multi attack (seeker).
The Plasmagun is pointless aside from being projectile based instead of hitscan, so it needs something to really make it worth while. Having the BFG be a super-mod for the Plasmagun is a good start (freeing up another slow), while having stun-bomb return (why this was removed is beyond me).
That leaves the Gauss, which shares a lot of commonalities with the RPG. Both are high damage, the only exception is one being spread and the other being a high damage 'focus fire'. But we already have that with the sniper shot. So let's turn the sniper shot of the HMG into a lasershot that's hitscan.
Then there's the two shotguns. Why are there two to begin with? One is a grenadelauncher with a single fire, the other is a double barrel with a mobility extension. We've just freed up a ton of space on the keybindings by combining weapons, so the grapple can become its own button (no shame there, perhaps also allowing it to pull enemies instead of pull you). So we can make the default shotgun a pump action (high spread, low damage), alt fire doublebarrel (low spread, monster damage) and the mod-fire the sticky launcher.
We've just combined all the weapons and lost nothing of value one could argue, opening up a lot more options for more unique additions like a piercing weapon, damage over time, stun, decoy, mines, flamethrower, gravity etc.