A friend was raving about Doom's single-player, so I caved.
It's... good. Not great. So far. I'm through the first 3 levels. It's definitely better and more Doom-like than Doom 3 was... but I still don't feel it lives up to the legacy of classic Doom.
I still can't get over the generic feel of the creature designs.
It's fast-paced, but in a weird way that's sort of difficult to describe. There's not much emphasis on fast-paced movement, so much as twitch aim, because many of the monsters engage in a lot of vertical movement. You don't really do much dodging or make use of cover, and there's extremely heavy focus on melee. You move from one monster to the next. Take some damage as you run up to monster while firing a couple shots to put them in stagger, glory kill, gain your health back from the drops, repeat. It does make for a sense of relentless ferocity to your character, but it leaves out everything that made the combat feel of Classic Doom satisfying.
And I seem to be in the minority on this, but the glory kills are getting old. I think they'd be fantastic if they were like in Brutal Doom - something you have to go out of your way a bit to do and involves some risk for purely aesthetic reward. Instead, the gameplay encourages you to glory kill every single monster. They're literally how you keep your character alive.
Then there's the level structure. Everything's very compartmentalized. Each fight is a singular carefully designed scene with distinct breaks in-between. They never bleed together. You walk into an area and trigger a bunch of monster spawns. You're not allowed to leave the area until you kill all the monsters. Exploration/story bits in-between. This really drives a modern interactive story feel instead of feeling like a game. Some of Classic Doom's most interesting levels were the big open ones where you could get all the monsters of the entire level chasing you all at once if you weren't careful. You had to deliberately work to keep a fight contained and manageable.
So... eh... gonna keep playing. Just my observations so far.