I have to echo people who are saying that this game feels tailor made for them, I feel the same way. I've put in about 35 hours or so, done one full UV playthrough and am about halfway through Nightmare, and I'm in love with this game in a way I haven't been since 2016 came out. That said, I can tell this game is really divisive (especially after seeing the duders talk about it today on the bombcast), and I can understand why.
The biggest thing I see people really disliking outright is the tone, while I feel like its what I want from a DOOM game (stylish but totally irreverent). I did not like the gritty look or feel of 2016. The things that I liked about 2016 were it's callbacks, jokes, and arcadey gameplay elements, and felt that the grittier art style served as a sort of disguise or smokescreen over the game the devs actually wanted to make. It felt much "safer" for lack of a better word. I genuinely love the goofy art style and writing of the DOOM Comic, and the modern DOOM game I've wanted since before 2016 came out is one that embraces the series as pure arcadey camp. I totally understand people being disappointed that this is essentially what Eternal does, even if I'm still sore from Jeff comparing it to Duke Nukem earlier today.
I do think, in contrast, that certain gameplay elements are getting a needlessly bad rap. For example, I've seen a lot of people in this thread and in general saying that the monster weakness system is overly restrictive and that each monster has a singular good solution, which I disagree with a lot. Take the Cacodemon. The most obvious way to deal with him is via the swallowing explosives trick, and you can do that in two ways (the shotgun secondary and shoulder frag both work) depending on how close the Cacodemon is (the shoulder grenade in particular has a short range) and what kind of ammo you currently have. But that isn't the only way of effectively dealing with them, for example, the ballista will two shot Cacodemons (at least on UV, I haven't tried it on Nightmare yet). You can also freeze bomb the Caco to stop them from pressuring you or unload on them with a high DPS weapons, you could blood punch them to falter them and take half their health off, or you could just blow them up with about 3 rockets.
All that said, overall I'm incredibly happy with the game, and while it does bum me out to see people not enjoying it as much as I do or as much as 2016, I respect the hell out of Id for making such a bold and strange game, even if it has alienated some people.