While I agree with his assessments of the first novel for the most part, he picked the weaker of the two best covers. I think the 3rd cover is a stronger illustration than the 4th. From a publisher's standpoint the 4th is better (it's more likely to grab a kid's attention), but as someone who knows the story the 3rd is less cartoony and a better representation of the tone of the story.
An example he doesn't show is all the previous covers from The Great Cow Race. Here they are:
This is the first cover. It has nothing to do with the titular race, but it is a pretty good moody piece that accurately represents an important part of the story. See the Scholastic version of Vol. 3 for a piece that botches the mood of these rat creature confrontations in the forest.
This is the 2nd edition, and it's pretty good. We can clearly see that this is the race, all three bone cousins are visible, and you can even see some rat creatures in the back. The colors are strong as well.
This is the Scholastic cover for the current edition. It's actually one of the better Scholastic covers, and is a pretty good contender for best cover of the three. It doesn't feature the shortcomings of the other Scholastic covers, like Bone being to huge and cartoony, or inaccurately depicting the scene as light-hearted (again, see Vol. 3 below).
Volume 3 has an odd assortment of covers.
This is the first, aaaaaaaaaaand it sucks. Even in the story it's not clear how these dragons are important until the last issues of the entire series, so this is a poor choice of image. Plus, I never liked how Smith used dragons that looked like they all came from different universes. There is little visual continuity between them. You've got the Great Red Dragon, who is purely Smith, then you've got a cartoony Puff lookin' guy, then Serendipity, then some flying dragon who is closer to Smith's own style but not quite. It's also very static. These are the most boring dragons ever. Bleh.
The 2nd cover, and my favorite. Features one of the best scenes from the book, which also happens to be one of the finest illustrated sequences ever put on paper. Fone, Granma, and Thorn are out in the woods in a lightning storm being stalked by rat creatures, and Smith manages to pull off perfect tension and suspense with black and white ink.
The coloring on this one is a little wonky. I don't know about the weird bloom effect. I guess it's supposed to evoke the light mist on all surfaces from the rain.
The Scholastic cover I keep referring to. Now, this depicts the same scene as the cover above, but look how much less dangerous it looks! Granma Ben is already pulling up her sleeves to fight the rat creatures, and who wouldn't? They look like dorky bats. The second cover made them look like true monsters, like shadowy menacing beasts you should actually hide from.
Also, Bone is huge and ruins any chance for decent composition with the other characters. And get this: this is the guy's favorite cover of the entire series!
This one is not great. It's ok. It's a striking image. But the lense flare is taboo in modern design. It doesn't speak to the story as well as it should. It's better than the Scholastic version, though.
Kid friendly, sure, but Fone's pose is stupid, Lucius looks like a pathetic wimp, and Phoney is doing the "in your face!" thing again. Stop it. Show me a well-composed medium shot. The Bone characters are so simplified in their depiction that you get no sense of Smith's beautifully detailed line-work if you take half the cover with a Bone face.
Here's my favorite cover of his, from one of the comics. It's gorgeous.
Now THAT is composition and coloring. This is a design that will make me pick this thing off the shelf. This is a design that will intrigue me about the story. This is a design I want poster sized for my wall.
There will be more to come as new covers are released, I'm sure. I'm actively collecting the out-of-print HC editions of the Bone series because I don't really care for the new smaller color versions. The old black and white books showed off Smith's line work better, and you weren't distracted by the colors. He achieved mood and painted the scene for you in only two colors. He didn't even use any half-tone. A master.