Is it for a graphics class? I didn't read the first part, so I didn't know you were being graded on this. I'll offer some constructive criticism. Here are some things you could improve on:
Fix the Animorphs proportions.
They look like they've been stretched in width. Look at the original picture as a point of reference and try to stretch the height of the edited picture to even them out.
Normally I never change proportions of a picture I crop or mask unless I really have to. If you're doing this in photoshop, then the Shift key is your friend when using the transform tool. In this case though, you can easily fix this by stretching their height and you don't necessarily have to start all over.
The Blending of David's eyes with the Background.
I really think you could work on this part a bit more. I understand trying to bring out David's eyes, but there should be a natural blend with this and the background than what you have going on now. It'll definitely improve it professionally. You can do this in a variety of ways (layer blends, opacity settings, masks, etc)
The Subtitle 'David's Trilogy'.
I would fix either the location or the emphasis of this on the cover somehow (font, background box, etc) because it's really squished under the Animorphs title, and doesn't really stand out in any way to focus on its importance.
At the same time, you've made the size of both the subtitle and the tagline the same. I would change tagline to something a bit more smaller and out of the way (though that part is just a preference of mine, it's really up to you).
Edit: I just saw you posted before me, so everything above was for your first cover.
