The black header looks strange because the rest of the page is very light.
- less constrast
- logo is good but I'm not sure it will work the same over a white background
Here my first few impressions:
About the part just below the header :
- in the text, emphase done in black seems "bizarre" to me
- the monitor looks good, maybe the screen has too much shadow
- the banner is good & convincing
- the button are too dark and the text shadow shifts too far
- the color of the button goes with the background found in the monitor, what happens when the background change?
- I'm not sure about the button color (complementary color).
- I think that only the download button (with last version number somewhere) is required. Overview is already visible in screenshot section & header.
- I'm not sure the wave separator is the best thing. That's what makes it more "casual".
In the screenshot section, maybe a link to "overview" is required.
There is no blog link in the header
There is no about link in footer. I'm not sure an about page is required, since the frontpage can do that job.
There is no mention of guix package manager.
Maybe doing a mockup including a FSF campaign banner, to avoid akward design in this situations.
The overall looks very good. It's looks unique & modern. The page is not too large & the font size not too small. Very good job. Among all the above, it's really the complementary color that looks odd. It has its strength, but it seem old fashioned to me.