So, finally finished it.
The game gets a lot better once they stop bombarding you with collectibles, rune trials and assorted shit every five steps, especially the rune trials are a crime against any kind of tension and pacing. Still, you get plenty of time to play with all your toys, they avoided the ugly habit of giving you the last upgrades 5 minutes before the end. Story gets the job done, no complaints there besides the forced exposition scenes which have no place in Doom and it gives a good backdrop to the action. The level design also improves over time, the hell levels are exactly what the game needs more of, since the space base ones feel like replaying Lambda Core. Still, the arena combat clashes with it heavily - no pickups = no enemies. Especially with the amount of pickups the game showers you with, there could've been a bit more unpredictability. I don't think I ever entered an arena without max health and ammo. Couple that with the chainsaw, which is a free demon kill+ammo refill and every enemy ejaculating health once you drop below 100 and every arena having a powerup, it feels like the deck is really stacked in your favor. Might be required at higher difficulties, but I felt really railroaded in how I approached the combat. I'd rate it about as good as the new Wolfenstein games, less open, but more guts and slaughter.
Now let me gush about the graphics and enemies for a bit. The last game where I started giggling while plowing through my enemies was Brutal Doom, picking up berserk here had similar effect. The detail, animation and size of many later encounters makes them really satisfying to kill, which is what makes this game so good. The design of Hell levels is absolutely breathtaking and since they could drop all logic, some of them almost evoke the atmosphere of the classics.
With the ending, I'm really annoyed there's nothing else for singleplayer. I feel like they could drop the overdone arenas and then sky is the limit when it comes to combat. I suppose Snapmap was made to fill that gap, but the enemy/prop limits kill a lot of creativity - I suppose that's also the reason behind the arenas, consoles would melt if they had to render 20+ enemies at once. Still, if you want more of the same, go play the remake of Shadow Warrior, better level design, smaller budget and also an awesome shooter.