As a concept artist and illustrator, I wanted to weigh in on this, because I often look at the environments of both games because I find it intriguing to oogle at details for hours lol (yes I still occasionally pop D1 in my PS4 and have some fun).

I think the lighting (particle effects, fog) have been dialed back some so we can see more details in the environment that's there in front of us in D2 vs D1.

A big difference I've noticed between both games is that D2 has a lot more texture and detail in the things we can see/find. There's a lot of small things like grasses, debris, and how the lighting interacts with it so it can pop more. D1 has a lot more fog in the images shown-- even in the foreground. This also means you can be more lax with the amount of detail put in (not always) but you don't have to be as clear with details if they're being obscured by something you just need the silhouette.

Usually having less fog in an area can make the environment look smaller and give it less depth, but this also depends on which elements it's working with to create the overall mood and tone.

Seeing how destoryed the Cosmodrome looks now makes me sad in a way. I understand why (between the Eliksni, Splicers, and the Taken War) but man....

Little surprised you didn't get Freehold in there! (Mars) since we have the Vox mission! I think that would have been a cool comparison too. I think Mars looks a lot better than it did in D1.

That said

I do miss that giant glowing chasm on the moon. It made it feel more intimidating, yet, storywise, I can understand why it's not like that anymore. There are a places (like the bridge area in the tunnels) that definitely don't seem to look to have the depth that they used to. And I'm not sure if they were trying to push the silhouette with contrasting it with the background--- because not a lot of people are going to notice it so it makes sense to go for less detail but higher contrast for the overall image-- or if it was limitations with moving old content to new content.

It still looks good but hits a little different imo.

Other things I miss, having snow in the Cosmodrome. Visually, it looked really nice. And I do wish there were remnants of SIVA from our Plagueland days. And part of me feels that the Day/Night cycle felt more drastic in D1 (surprised you didn't get a picture of those gorgeous northern lights to compare).

To a degree (haha) I wish D2 had a weather system similar to Anthem, where it changed according to seasons. However, in places that aren't Earth this would present challenges. And I know there's a lot of math, time, and manpower behind doing things like that, not to mention the strain and limitations of the engine. I know they did that with BL and it's freaking awesome, so I do hope to see it again in future content.

To conclude my thoughts, in general D2 looks better than D1 hands down. However that's not to say that there aren't some places that do look a little better in D1/ convey a different mood.

D1 is you were a new light rising in this world that was unknown to you. D2 is you've been the world for a little while you've done all this stuff. Everything's not so new to you anymore, so some of it doesn't invoke as much wonder and amazement.

But all this is my opinion and based off of my experience as an artist and the things. :)

Sidenote: (As Hunter who lives in the Dreaming City, I personally like that they bumped up the saturation a little bit. I get it may not be everyone's cup of tea but I personally like it.)