(A review of the singleplayer only.)
No cover system, no regenerating health, no weapon reloading, and no mercy. If that doesn't sound appealing then this isn't the game for you... This an old-school game with some modern tweaks, fast and twitchy acrobatic violence with heavy metal in the background, that makes every room feel like a dance of death.
The enemies are all enjoyable to fight against and require you to mix up your attack style accordingly, and the weapons are all perfectly balanced and customizable in interesting ways. There are a lot of them, but they're all powerful and effective, and all useful right up to the end of the game. The only exception is the pistol which is a pathetic peashooter against anything other than the most basic enemies, but it has unlimited ammo to compensate for that. Almost everything in this game is satisfying in some primal "lizard brain" way. The game even makes your deaths satisfying, because you can get killed in creative gory ways that are just as funny as they are horrifying. I also love the way the story is everywhere but is optional at the same time, and how the exposition can always be ignored. Doomguy himself expresses contempt for the story, by smashing screens when people are speaking through them and by ignoring instructions. Clever and funny, and emulates the attitude a lot of players will have.
It is a challenging game, so you should expect that, but it honestly has one of the best difficulty curves I've ever seen. The way that it steadily introduces new concepts, new weapons, new enemies, to both empower you and challenge you at just the right moments, is masterfully done. At first, a new enemy is a big scary threat, and you'll scramble around trying desperately to defeat it without losing all your health, and that's before you even pay attention to the weaker enemies in the room... Later on though, they become the weaker enemies, the type of which you'll effortlessly get rid of after you've focused your attention on the new big scary threats. Your progression to that point feels completely natural, the game always hits that sweet spot of being challenging without being annoying or overwhelming, and it never once seemed unfair on the "Ultra Violence" difficulty level. The delicate balance of the difficulty, and the steady progression of the action, are probably my favourite things about the game.
I don't like how the game is so focused on arenas full of enemies though. There's a predictable loop where you'll walk down a few corridors, maybe listen to some exposition, kill a few token enemies, then enter a large room where dozens of enemies will spawn, and the doors will lock. You'll kill them, then more will spawn, and maybe a few more after that. When they're all dead, the doors are unlocked and you can proceed to the next corridor... Rinse and repeat, for 12 hours. The gameplay is satisfying enough that this predictability wasn't a huge problem for me, but it does get tiresome and it feels too formulaic. The old Doom games had moments like that, but overall they weren't really about that. The levels were usually more open with demons everywhere, that you blasted through to get to the exit, and you could usually retreat through the sprawling level design and take different approaches to each encounter. Doom 2016 is like the old Doom but mixed with Painkiller or Serious Sam.
So I found it a little predictable and repetitive at times. But overall it's really satisfying, simple brutal fun with some clever design. A breath of fresh air to come out of the "AAA" industry.