critting graffiti is hard
first to start out with a positive: your choice in colors and execution of the fill was nicely done, i especially like the highliight lines at the top of your letters.
some things to work on, would have to be formost your letter structure, try to make your letters look more firm and less like blobs, the puffyness of the letters need to be offset with some hard edges and defined bars. Also when you do letters that "squint" to one side it will create the illusion of perspective, when this happens make sure to treat your 3-d accordingly. in this case it should be angled to the right, not the left to make the image jump forward. or if it was to stay to the left it should be more left and less down. these are just a couple things to think about the next time you sit down to do a piece, I would strongly recomend doing font practice you can find thousands for free over at dafont.com copying fonts in graffiti style will be the fastest way to learn the things ive mentioned above...good luck