Great brush! There are some areas that could use a tad more work, but we'll get to that later
First let's start with the design, which I think looks awesome! One of the cleanest Golf's I have ever seen. The bodykit really works well with the overall body of the car, making it wider and more agressive without breaking the overall lines of the original car, or making the car look modified. It has sort of an OEM look and feel to it which is really nice! This is also strengthened through the overall design of the bodykit and how the pieces fit together. The little wings on the sideskirt appear again on the back bumper, and it all seems to be thought through and fit together. Really nice work. I also like the black pieces you have added as contrast, like the venturi, the wing and the mirrors. You can't really see it on this picture, but I think this would look awesome with a black hood to connect back to the other pieces. Would be awesome if you could do a front view version of this chop. What you would do would be to find a picture where the car is in such an angle that you can put the front wheel at the back, and the back wheel at the front. Then brush it using the same donor

Would be sweet and would defenetly promote you to PRO
If we move over to the execution, I think the side looks amazingly good. The gloss and depth in the paint is awesoome, and it looks really realistic as well as having a nice atmosphere about it. My main issue with the brush is the back of it. It looks a bit flat in the colors compared with the side. I would have liked to have seen a bit more depth there, and with depth I mean contrast. The back should have been a bit darker, and then rebrushed the horizon line again to make it look more like the side of the car. The second issue I have is with the door lines, but I have the same problem when it comes to making them not be toony. It's really hard, but you have managed quite well on the side, but the door line furthest back is the main issue. You have erased the line a bit much at the top of the door there. Wish I had a great solution for you, but like I said this is an area I have some issues with myself so... I'll let you know when I know sort of. Hehe.
Overallt his is a great brush! Expecting great work from you in the future

Cheers!