Finally finished this game the other day. I really liked it overall and think it's more fun than Doom 2016, even though it definitely took longer to click. Combat-wise, I still think it's a bit like Sekiro in that while the game's design does want you to play in a certain style, it gives you a good amount of wiggle room within it, and the game's focus on it really lets that style shine once you embrace it. The game is a joy to play once you really get used to the huge toolset that you've been given. You really aren't just swapping between two guns like in 2016. By the last level, I was using nearly every gun in the arsenal, and hot swapping mods for the rocket launcher and chaingun too. You can pull some insane shit in this game that simply isn't an option in any other FPS. There's nothing that I know of that plays like this.
The last level was amazing because the big rooms were like doing Slayer Gates back to back. The game just doesn't stop throwing shit at you, but you have all the tools and experience to fight it now. I loved it, except the actual final boss was a drag. I get that it was kind of trying to be a throwback to the Icon of Sin in Doom 2, but it was the type of boss that doesn't really jive with the game's combat flow, and really suffered for it.
Couple of stray thoughts:
I kinda liked the story for what it was. It tries to go for the same tongue-in-cheek dark-but-dumb tone as warhammer 40k, which works for the series. I disliked the time skip from 2016 - I felt like it was a good setup that got dropped for some reason or another during development. What we did get was okay, though it told the story of the Doomguy in an unnecessary amount of detail, and retconned key characters like VEGA and Hayden pretty badly. There has to be a reason why the developers went in the direction that they did. I liked the story of 2016 more overall - as a whole it was just tighter, and I liked it better when Argent Energy was some unknown dangerous crap that humans named themselves, and were using without understanding the consequences. Eternal establishing it as a godlike energy source used by advanced races diminished the feel of it.
I think the weapon balance was FAR improved from 2016. Almost every gun had a role, even in end game. The only guns I wasn't using much by the end were the default shotty and plasma rifle. Everything else was good for something. I really liked how they improved the chaingun, since it was a disappointment in 2016. I'm sad at the removal of the Gauss in Eternal, but I also understand because it was just too strong and trivialized many other guns by existing. I do think some mods could be tuned a little bit better, but it's a minor complaint, and I think all in all they did a fantastic job of balancing them this time around.
I'm okay with the marauder. He usually meant at least one death in every arena where he showed up, but I didn't find him too oppressive. He feels a bit like a dark knight in a Souls game - beatable once you know how to fight him, but can still kill you singlehandedly if you make a mistake. It makes him a unique threat because by midgame, you can reliably 1v1 pretty much any other demon in the game without dying.
Combat-wise, the marauder functions similarly so a super version of a Baron in that you're basically supposed to run from him until you can fight him on your own terms. He's a wrench that's used to escalate the combat in the game because the roles of many other enemies have already been exhausted by then. Some enemies chase you to keep you moving (knights, barons, stalkers, whiplashes, etc), some make you go to them to shut them down (carcasses, archviles), and some try to deny you space (arachnotrons, cyber mancs). After those things, there aren't many options when designing a new super enemy because you can only get so tanky or damaging before it feels cheap. My guess is that's why id gave the marauder its unique mechanics instead.