Dude, the best advice i've ever gotten from graffiti, is if you know its not good... don't post it. Some people disagree, but when it boils down to it do you want the doodle you did during class critiqued? Or do you want the masterpiece that you tried your hardest to perfect, it might hurt more to get the second one critiqued, but you'll get more helpful tips because they'll really point out your weak spots.
I'm not gonna lie, artistically, its kinda bland and not to creative... Kinda reminds me of one of those things you try and see the hidden image. I haven't seen your other work, because I haven't been here in years, but my advice would be to try start simpler, follow some tuts, and when you get those under total control try branching off and finding your own niche. It might be different for GFX, I'm just saying what is said commonly in the graffiti world.