The following might sound negative but my intent is to provide some useful feedback. It's only my opinion, I don't pretend it's the truth. I'm not a designer or web developer and my own website probably has some of the problem I mention.
I think your site doesn't look good, and isn't setup for a good reading experience. I'll only talk about the dfpsr page, but it applies to all the site.
When I first arrive after following the link, the main visible thing is the screenshot. The image (and text) is left aligned. If the browser is maximized, it doesn't feel comfortable as I'm centered in front of my monitor and the right half of the screen is just black and unused. The screenshot itself isn't interesting to me. I understand it's suppose to show what the engine is capable of, but it's dark with no atmosphere, the scene isn't interesting, the lighting isn't interesting, the composition doesn't exist and the format isn't interesting (the image is almost a square, you could use a widescreen format). The integration of the engine (or is it just a renderer, that's not clear) name isn't good and should be more stylized (~logo).
In my opinion you should center the content on the screen, use only a portion of the available width (have a max width a 1024 for example) as it's easier to read text if it doesn't cross the whole screen.
The menu doesn't look good, the separators don't look good, the green on black colors look like all the sites that were created when The Matrix came out. It seems you're going for an oldish style, but in my opinion it doesn't look good and makes me think that the content of the site is old and was there for the last 20 years without being touched. I think you should go for a lighter (well just not black everywhere) theme, and a bit more diversity in color for text and UI.
The text itself isn't that useful. It's not clear to me what the renderer provides feature wise, for whom it is created, for whom the site is created (user, or contributor). The first paragraph is a bit weird to me, it seems like I started to read in the middle of a larger paragraph.
The following line doesn't make sens to me:
Want a custom rendering pipeline or image format? Just copy and paste until you have found a unique style.
The following seems suspicious. It seems to me that you're saying that if you throw stuff at a GPU without any care it will work worst than a well thought out solution on the CPU, which isn't a fair comparison to me.
2D and isometric graphics that a GPU might struggle to render in 60 frames per second due to a poorly utilized 3D graphics pipeline and call overhead can be drawn in 300 frames per second on an affordable desktop CPU without messing up your code.
Overall you seem opinionated about GPU vs CPU and Open Source vs Proprietary, which is OK but can come out wrong and discourage potential user.
The banners you provided will most likely clash with any other website and I think almost no website uses that kind of things nowadays. Press kits contain higher resolution images that publications can edit to fit there layout and different logos that fit with different backgrounds.
As for tools to create a site I like the ideas in this post from Fabien Sanglard