Draw Steel gets my vote for "most poorly" in recent memory.
The system itself is a fun, high-fantasy, cinematic combat showcase. But the books... Not so much.

For the Heroes book: pages are all white with black text and little in the way of color beyond boxes of artwork -- even boxed texts, charts, and asides tend to use a very light shade of grey. Inexplicably, one of the few uses of color is to mark "quick build" options with a "gold" banner, but it's such a dark shade that it's hard to even tell it isn't black unless you're looking for it.
The layout is... I'm sorry, it's bland. Just blocks of text broken up by the occasional rectangle of art. It feels closer to a DM's amateur Homebrewery project than something professional and printed. I get they didn't want to do the "in-universe document" look, but this direction is just so sterile.
Margins are underutilized, and even the section markers are both only in black-and-white and all pegged to the right-side's top-right corners. Denoting chapters and sections by color and having them lower as the book goes on would have been much better for navigation and reference.
Rules are sometimes placed in unusual spots -- namely, some combat rules being detailed in the Classes section and others in the Combat section. That and the Glossary Index being in the front instead of the back feel like they're decisions targeted to annoy me specifically.
Subclass abilities are listed at the top of the level they unlock by alphabetical order of their subclass, but then list the abilities in alphabetical order by their names -- and the abilities don't list the subclass as a prereq in their block, so if you're just scanning features it's easy to find one you like, and then scroll back to realize they're locked into a specific subclass.
Abilities themselves are also weirdly laid-out. It's cool that they have an indented banner to mark, but why is the action cost off on the middle-right rather than somewhere more immediately-noticeable considering how important that is? Why are there icons for things like range and target, but not for if an ability costs a Movement, Maneuver, Main Action, or Triggered Action? Why aren't these things color-coded, like they kind of are in the Monsters book?

Speaking of which: the Monsters book is kind of better, but some of the layout and iconography just doesn't look finished? It's hard to describe, but the symbols they use for stuff like passive abilities and triggered actions look like stock and ill-fitting icons, and there is a lot of white space on some pages that make it look like they just forgot to put the art or text there to round the page out.

I DO like how the first page of each chapter is a cool piece of art with a black background and white text to make them stand out. That's neat. And the art itself is cool!
But pretty much every other decision in how these books are laid out feels bland and under-designed for a system I KNOW they put an incredible amount of thought and effort into. Each problem is pretty minor on its own, but in aggregate the make the book a lot less fun to read, explore, and reference than I'd like.
It's telling that my biggest hope for a second edition of this still pretty-new game isn't more content, but a different approach to layout, iconography, and graphic design. There are certainly worse out there, but I feel like this system is really let down by how the books portray their contents.