I think its good. You just need to get the colors right with the characters. like their skin color.

Gimp user here o/ Although I'm not one of those super freaking epic poster makers, I can give you some feedback.

I think you have the main idea of all of it, but I think what you should focus on most is making everything flow together and seem the "same" if that makes sense.
For "the mystery girl" poster, I think the girl is a little too soft looking, like her opacity is really low and such and doesn't really match how strong Zelo's is. I'm guessing you're going for a faded look, but to some it might look awkward because it's too soft and the pictures don't seem to go well with each other.

For the first poster, this is just a personal reference but I think textures look best as like...something to make the main pictures stand out, or to fill in spaces. you don't exactly want a texture all over the persons face, because sometimes it can look a little messy and awkward.

And one last comment, I think you should play around with the typography more. I like the font you're using, but for majority it's kind of hard on the eyes and a bit hard to read. Sometimes more simple fonts can be best, is what I think.

But overall, I think you're doing pretty good! You definantly go all out with all of these posters, so don't let my comments let you down at all :D
I hope I didn't come off as mean or harsh, but rather than my comments came off as constructive criticism :D
If you need any help, feel free to come to me, i guess haha

Browse the gimp tag here in aff.

http://www.asianfanfics.com/story/view/154324/gimp-innovations-poster-gimp-tutorials

Your posters are really good! I'm a beginner as well so, not much help! xD Hmm, I think for your last poster, the font for the title is a bit too swirly and stuff. ^^
They're all really well done~

i think you should use more textures that are soft and don't have so many designs and stuff on them. ^^ it'll make your posters have less of those lines and stuff when you have your final result and it you still want to use those types of textures then i suggest you erase some of the texture around the characters faces so that you can see their faces better. ^^v and for blending (since i also use gimp) lower the opacity of the brush and erase some of the parts around to give the characters a better shape instead of a square with erased edges. ^^ (don't worry, i used to do that all the time too. >.<)

the posters are definitely good!

The Mystery Girl . . . damn that's an amazing poster!
I think they're all really good, but the subtext in Mystery Girl needs to be a tad darker, beacause it's slightly hard to read :)

The Mystery Girl... I don't know why I misread that as gift XD

Sorry that I don't know anything helpful, I just wanted to say I freaking love the posters you did post in here XD. Especially the one that says "The Mystery Gift."
You already seem like a pro to me xD.

When you write down the person's name and your name...it kinda ruins the WHOLE thing O__O

sorry if that was mean but we can always talk it out XD