Ok, now that I've had time to mull things over, I'd like to give my detailed thoughts:
- The Doom Slayer still has the Praetor suit and it appears upgraded, but he lost the sleeves for some reason. I'm happy the Praetor Suit hasn't been ditched, but I'm hoping the story/lore provides a reason why he ditched the sleeves. He does look a bit beefier in the concept sketch now - almost too beefy, but that's a nitpick.
- SSG grappling hook along with the added movement appears to work well and could add new layers to both combat and exploration. I like.
- I love the environments. I mostly stand by what I said earlier that Hell on Earth looks like it should, with some surprises (the good kind of surprises, where you almost wish you'd thought of it yourself).
The only beef I could have so far, is that very little in the city ruins jumps out at me as being "really high tech and futuristic"; there's some glowy pillars and flashy billboards, but on closer inspection, that mostly looks like stuff you could see today. At least the car wrecks don't look like cars from the 1980s.
- Classic redesigns (monsters and some items). Not sure what I think. The Classic 1990s Doom fan in me has a massive nostalgia-boner, but the Doom 2016 fan in me is a little annoyed they apparently ditched what I thought were fresh and good-looking redesigns in the Doom 2016 title.
The new(/old) Mancubus seems like a completely different demon from the 2016 Mancubus (but with the exact same behavior/abilities) and I find that rather jarring. I can only hope that the game's lore provides a good reason for the sudden, massive change in appearance.
I have similar thoughts about the new Possessed Soldiers, who at first glance look redesigned just for the sake of nostalgia-pleasing (although I do like them a lot), but seeing as the 2016 counterparts were created from what the game called a "Lazarus wave", the new possessed could have become possessed through different means and that would be a good explanation (though it doesn't explain why these guys are out of uniform; that is why they forgot their helmets...).
I will say though, that I like the redesigned civilian possessed; they found a neat way to have civilian enemies that are easily identifiable without having to do a million different models for different clothing and such to make them more confusing to pick out from the crowd - this is essential in a fast-paced shooter like this.
I like the classic-looking medkits and health potions, but again find it weird that the perfectly functional and good-looking argent stim-pack designs of 2016 have been ditched. Again hoping for some lore explanations.
- New monsters. I quite like the monsters seen in-game, the look of them at least. The winged gargoyle-thingies don't strike me as out of place. I haven't seen any attacks or behaviors that strike me as game-changers though. The gargoyles seem mostly to function like Scrags from Quake 1 (i.e. Cacodemons, except these are squishier).
The Arachnotron seem to be lobbing plasma-based mortar projectiles (I don't know what's supposed to be special about those, but they might have some yet unidentified qualities that make them special), and I'm not sure I'm completely sold on it's lack of "laying-down-walls-of-plasma", but who knows how it's new behavior will actually affect gameplay in the final release? I do like its spidery movement animations and its ability to cling to ceilings and walls. Yes please.
The most interesting things about the Pain Elemental so far is that the Lost Souls it spawns hovers around it like a shield of sorts and that it will occasionally grab one and toss it at the player (but the classic "spit-it-at-the-player" attack also seems to be there). The Lost Souls don't appear to home in on the player though. Could be a good thing, but it could also make the PE feel more like "just another cacodemon", which I'm not so sure about.
I did not like the concept sketches of some of the new monsters - they look out of place and not very Doomy (referring to the "floating hover-tank skeletal Demon thing with a chainsaw hand" and the "Hell Knight thingie with an SSG").
Glory kills and other special attacks. They reused some animations, though on closer inspection, some of them have the minor change that they incorporate the Slayer's new wrist blade, which makes it a bit more ok. I did notice that there was an Imp glory kill that appeared to be exactly the same as in Doom 2016 without usage of the blade. Still slightly disappointed about the re-used animations. Fortunately, there seems to be quite a few new kill animations to along with the existing ones.
I do like that you can apparently do stuff like cause a Cacodemon to swallow a grenade, that's pretty sweet.
It took me a while to figure this out, but it appears that equipment items are launched from the Doom Slayer's Predator-styled shoulder cannon, which is nice. I was surprised to find that I liked the flamethrower-attack a lot, as I've never been a fan of the idea of a flame-thrower weapon in a Doom game (not sure how to explain why - something about it perhaps occupying the plasma rifle's particular niche and me just not been feeling it), but it works as an "equipment item" that "stuns" enemies, allowing you to finish them off with regular weapons; it's always awesome when a developer manages to implement a concept I'm not a fan of, but do it in a way that I can totally get behind, while pleasing those I disagree with.
New weapons/weapon makeovers: In the end, I'm pleased to see that we won't be using the same pump-action shotgun we did in Doom 2016 (gives me a reason to still go back and play Doom 2016 even when this shiny new Doom game out).
They're keeping the classic Doom gun concepts, but you're still using different ones and with mostly new, or at least improved, alt-fire modes. Like the Doom 2016 arsenal, the visual designs are a toss-up; some I think are really cool, some I currently think are a bit silly (Hell Rocket Launcher? Hand-held ballista?). The sillier designs might grow on me - after all, it's Doom, it's supposed to have a healthy dose of silly.
The new Plasma Rifle is a superb re-interpretation of the Classic Doom weapon, but I could nitpick that its design has the same weakness as the classic weapon: it does not look very practical. I do like that this version is bigger and bulkier like a massive general purpose machinegun type weapon and not so much an assault rifle (I like the assault rifle design a lot, but change is nice as well).
They appear to have addressed the issue of the Doom 2016 Plasma Rifle where it's primary fire became next to worthless late game, as this new one appears to have sort of an accumulated electrical field effect. I don't know exactly what it does, but it looks a bit like it creates some splash damage area-of-effect and does a bit of extra damage or something. I approve.
"Story elements": I like that they kept the silly holographic UAC representative spouting insane propaganda and it's nice that they made it female this time (for the sake of change and distinctiveness). The propaganda is in-keeping with the tone of the 2016 game, while still eliciting a few grins from me. Also, the UAC appears to have gone so far out insane that they actually wish to "terraform" ("Helliform"?) Earth to bring their "Mortally challenged Friends" over for a big party.
I was surprised to find that I was pleased to see other living, fully Human NPCs in the game (considering how well their absence worked in Doom 2016), but the scene where the Doom slayer walks through a control room with UAC employees who react to his presence currently strikes me as superb - I only hope that if this scene is in the final release, it will at least allow the player to directly control the Doom Slayer in this scene. If not, at least it's not too long and it is rather rewatchable.
I like that there's a BFG 10k in the game and it comes in the form of a gigantic, Quake 2-styled "Big Gun" turret cannon and that the Doom Slayer is on a mission involving it somehow.
I noticed that the Automap has a "Demonic Corruption" bar and I'm guessing it ties into how many Demons are present. It's a small thing, but I like that a lot. The simple idea that the Doom Slayer is slowly beating back Hell's corrupting influence on the environment by removing the Demonic Presence, while also providing sort of a classic-type tally of how many enemies are in the level. *Approval*.
Other observations: A lot of the item pickups appear a bit too cartoonish looking. I'm hoping that's only because the art is incomplete, because I find it rather reduces the sense of "I'm playing a CGI movie" that was present in Doom 2016. Shotgun ammo seems more inspired by the classic "4 shotgun shells" pickup sprite as opposed to the "Quake 2 style shell boxes" in Doom 2016. I like that.
tl;dr: 
- but with a few reservations about some jarring changes.
Edited by dsm
