I would say it is a very good attempt. Though I dislike the idea of "Radioactive" or "Toxic" weapons that put an emphasis on the colour green here and there. At least you didn't make it solid green and solid black.
I think you should keep trying. But it seems L4D2banana is pro territory, with hi-res skins and high poly models being submitted all the time. I suggest starting skinning with Team Fortress 2. The waters aren't as deep there. And the game is F2P, meaning there's a large audience too to give quick feedback.