The new site is even more javascript-dependent than the old one, so yes, it will be slow if your processor is slow. All the video material and high-res pictures will also slow down things for the less bandwidth-fortunate ones.

Look on the bright side, the GOG servers are doing alright. Probably seeing less usage, running at lower temps, generating less of an electrical bill. The new site is "aesthetically pleasing" and "in line with modern trends". All is well in the land of GOG.

I noticed the site is considerably faster on my old Iphone, it doesn't use any transitions and is less image heavy.

Anyway, here are some results from benchmarks:
https://gtmetrix.com/reports/www.gog.com/HLNYBQ6I Even if that were true in this case, I spent some time doing web front-end development in the past, and let me tell you that I don't even want to know what you are doing to max out the CPU on a high end 2015 device. It's not like a webpage is some AAA game. I might do some profiling and testing with other browsers to see where the slowness lies. I just haven't bothered yet.

I don't see any slowness outside of Gog responding to the numerous threads in the place about reported dislikes.

No problems of note here.

Nope, no issues here. And I'm using an old version of Firefox (52).

I find just this new design super slow and counter intuitive.

I think GOG is loading larger graphics and other scripts. I can barely even function here. Also, who the heck decided to not show what's new on the front page? You have to click a link/tab? WTH! I don't care what's popular.

Sorry guys, can't say I noticed any slowdown myself. However, I'm really not a fan of how spaced-out the layout is, though to be fair it seems to be a trend elsewhere too. It's annoying scrolling, scrolling, scrolling everywhere. First up instead of a header it takes up most of the page, right off the bat you're gonna have to scroll down to see anything else. Game details on one side, system requirements on another and you're gonna have to scroll some more between them.

I'm sure many find this style visually pleasing but honestly some of us crusty oldies prefer a compact layout. I can't help it, back when I was doing web dev 800x600 was the norm...