the light i'm talking about on the bike is in the original image as well as in the composite. look on the bit on the front wheel well, it's got a highlight. the backside doesn't, it's even darker in shadow. ignoring the reflections in the metal parts, you have same thing for the black part in front of the seat, there's a highlight, and on the seat, and along the top of the back tire and the saddle bags. there is light and shadow all along the bike that doesn't match the composited background because it uses 2 very small piece of the background that don't have a lot of differentiation in light. in your original image you have subtle light and shadows throughout the background that make a big difference in helping your brain and eye to make sense of the image and the light, but now those details are missing in the composite. it does sound like nitpicking, but when you go from a flat background to a 3d background with highlights and shadows it makes the whole thing more realistic. especially if you can make the background light match the light on the subject.