aesthetically, it's very appropriate, in my opinion. i like the colors, patterns and turtle graphics a lot. the cover bugs me, tho. i think the turtle should be scaled down to the point where it's feet don't touch the inner-most border design (leave 1/4 inch or so space, atleast). the arced text seems "off" because they're very shallow arcs in contrast with the arcs on the top and bottom of the turtle. the effect just "does nothing" for me and is a distraction. the size of the turtle left little room at the top for "la toruga's" which now seems crammed in there (presumable, (and correctly) because you didn't want it to overlap the head).
basically, i would have scaled the turtle down quite a bit to fit the text in properly. if the text was to remain arced, it would match the arcs of the shell.
also, i "see" the effect of the tortoise resting lazily on a sylized rug or blanket after a hearty meal

if this was intended, i would have rotated the turtle to the left ~20 degrees and let his feet cross the inner borders mentioned. a more haphazard "plopped down" vs vertical orientation.
still like it, tho. just my opinion here
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