The big thing that I see as a problem with your work is text. The text on all of the pieces is off the mark. The first two pieces are fairly decent but the colors need work because they're hella monotone and there is way too much going on to create any real sense of flow. The third is pretty nice but for all of the lines, because using random lines for the sake of random lines isn't a good practice because it really ruins the depth.
Another big problem that threads throughout your work is the lack of lighting or the inconsistency of the lighting on the piece. The skrillex pieces have some weird soft brushing, while the daft punk sig doesn't have any form of lighting from the light strokes which there should be, and the dark beauty is oddly washed out so to prevent any real use of lighting. While on the topic of the dark beauty sig, it looks bland, boring, and monotone. The softbrushings don't lend well to being effects how you have used them here. They create neither a sense of flow nor depth and the washed out look just doesn't work for it because it washes out whatever effect c4d you were using.