My initial thoughts after using it for a few days:
I think it looks very good, but I don't think it is as "clean" as the classic version. I know that everything is still essentially there, but it takes my brain a second to figure out what I am looking at. I felt the same way when the profiles were switched over. Like, I really understand that it's the same information reorganized, if you can even say it's reorganized, but it feels more "comfy" than "compact," leading to a lot of extra brain processing time on my end. I would like a "preference" setting where I can make it compact, but keep the same style.
I think the addition of popular collections is nice. I think the integration of collections into the main page of the game makes it feel more integrated. I think it was done perfectly. I don't need it more integrated, but just having the extra reminder that they exist on the page instead of the top bar is helpful to new users.
That being said, it does push down the mods listings, which is why I am here. I don't like having to scroll down to find the thing I am here for. Maybe just moving the popular collections below that would be better. OR, and I think this is where I land, I think you can get rid of the highlighted mods in favor of collections. May be controversial because what creator wants to lose discovery to a curator, but I think that just leaving the top two highlighted mods with making the banner a link to a "popular mods" section would be cleaner. Plus, you would then be able to literally see the "Popular" section without scrolling down.
The actual mod pages is perfect, don't touch it. I find the mobile dropdown menu to be awful and I don't know how you would change the current desktop iteration without doing that. As someone who uses this site a lot more that what I assume your average user does, I always forget that the dropdown menu exists and just give up when I am searching for information. Like, I KNOW it's there, but the way it's implemented suggests to my brain that the overview is the only page.
Somewhat going back to #3, just make the Popular section the default instead of new. I know discoverability is a thing, but I don't think we can have "everything" while keeping it clean and compact. Just swap the two. Most of the new mods are translations and NSFW mods (Jesus Christ Cyberpunk and Elden Ring) anyways and make finding the mods I want hard. Also, I can't figure out as a user what the difference between the "trending" and "popular" sections are, unless one is weekly and the other monthly, so I don't know if they are really doing their job. You could totally do away with trending. TL;DR - do away with trending and make "popular" the default view.