Not sure why the upright spines are double width ...
hum ... because it worked

(compared to my earlier, unpublished attempts)
the reversed U you used for shadows is a nice way to convey cylindrical volume while keeping a straight shape.
I was having trouble at first trying to sketch with your palette, and I think it's primarily because you've a huge hue-shift but little difference in saturation. I toned down the cooler colours and added a nice desaturated mid-tone to effect as a bounce light; the strong highlights seem to indicate a reflective surface so I ran with it, also spaced the values out a bit.
Thanks for the tip. I'll see to what extend the Nintendo DS tolerates that (there are pretty few colours available when de-saturating things as result of the low # of bit per channel) without introducing rainbow artefacts.
The new mockup looks great but I do miss the sense of architecture of the previous, ie, bg appearing as part of the structure of the fg. Probably this is just a result of a quick asset test but I'd like to see the owl perched on something of the foreground and the architrave appear to support a platform.
It's indeed mostly a test, and an in-emulator screenshot rather than a mockup, but there will be a parallax scrolling between BG and FG, meaning that the illusion of "supporting something" may be working differently in different places. I should be able to tweak the alignment of the planes to produce interesting architecture effect, though. I'll try to do that better in the next run.
In order to simulate depth, you could use contrast to make the perspective more obvious without compromising too much your style.
A good tip. I have to figure out how to apply it with this tiled hardware in a smart way, but I'll definitely give it a try.
you could have dents in the silhouette thanks to those "leaflets", instead of the clean curves; The cover could be thicker considering the size of the volume.
point taken.That seems to
vary from books to books, though.