Eternal is one of the most mechanically impressive that I have played in the genre so far. I liked 2016 because the pacing was perfect in the game, though I felt that the true potential of Doom was unlocked with Eternal. I love the old school Doom games as well, and the manner in which they translated that play style with the way the technology is these days, is very impressive. I have played a good variety of shooters and I will have to say that Eternal is one of the best ones I have played in the bunch.
There is a learning curve and I do agree in the beginning of the game, ammo management is a pain, so having to constantly chainsaw kill is a bit annoying. Though as the game goes on, especially when you get your weapon upgrades, and gauge your personal playstyle, it begins to translate very nicely. I played on Nightmare mode and I will have to say that the level of challenge is a nice change in the industry. It never feels cheap, it all is skill, and how well you understand the Doomslayers tool set.
Marauders are a bit of a pain when you first encounter them, though once you get the pattern down, they get a little easier to deal with. Though the thing that annoys me about them is if there was a bit more of a delay on the flash, then it would be a more balanced enemy. They managed to deliver traditional Doom in a modern Doom game. Which I hope that as the game ages, the modding community can really embrace it. It's one of those games that will age like fine wine, unlike other more traditional shooters. Just my POV, solid game.