Doom Eternal is all about gameplay. There is a story there and world building in notes but I don't know anything about Doom lore and i couldn't be bothered to read the notes and fortunately that didn't tamper with my experience at all, because it's a game with a 95% emphasis on combat and exploration. And it nails it.

Combat is extremely fluid. It makes you think fast and act fast. You're given like a million tools to deal with any situation and the best part is that you're not forced to utilise it all. If you want to by all means go ahead, but sticking to 2 or 3 weapons and mastering their mechanics is just as potent. I played on Ultra Violence (Hard) and I did just fine barely utilising using the railgun, ballista and the flame grenades. That being said, the game does encourage you to swap your weapons and mix up your options.
First of all ammo is limited and if you spam one tool you'll run out eventually. You can refill momentarily using your chainsaw on an enemy, but the supply/demand ratio doesn't really add up. Secondly, every enemy has a dedicated weakness; the fodder demons are weak but are often grouped so AOE is encouraged, certain enemy types are weak to the plasma gun, some enemies require headshots so using the scoped rifle is a good idea, etc.

Pairing that with the games emphasis on mobility, every enemy encounter is dynamic, fast paced and has you making decisions every single second. You'll be swapping from weapon to weapon, chasing fodder demons for health, burning up groups of enemies for armor and freezing big guys for breathing room. It'll make you feel exhausted and pumped for the next encounter whilst you go explore and platform your way through a mission. It's a satisfying gameplay loop and it's really fun because of that. I heavily recommend you do all the slayer gates because they demand you to play at max velocity and embody everything great about the games combat.
Also the music helps a ton getting you engaged and makes you feel like a badass but that's definitely been mentioned a trillion billion times.

The added emphasis on exploration and platforming is something I appreciated a ton. Coming from Doom 2016, where every level had a reddish hue and kinda looked the same, it was a breath of fresh air seeing all the different locales Eternal puts you in. The levels are all distinct and none of them felt like a chore to explore. You'll go from overgrown ruins of earth to an ice world to the center of hell. Levels are dense and have plenty of secrets and room for exploring and looking for upgrades. Mission/weapon challenges and the system where you get a upgrade points for beating an encounter encourages you to play differently and take up every encounter to not only make yourself stronger, but also give yourself more options during combat. Most upgrades don't simply boil down to "jump higher" or "move faster", but rather more like "you can slow down time briefly whilst in the air" or "dashes are immediately refilled after a glory kill"
Doom Eternal nails encouraging exploration by rewarding you with things that not only make you stronger, but adds to the variety in your arsenal and ways of playing.

And all that being said, the game goes on sale for like 10 bucks and it's on Game Pass. Just do yourself a favour and play it. !!