This was the original render (Fig.06); the next step was to do some post-production work to make it look more interesting
I used over sixteen layers with different adjustments like brightness, contrast, saturation and hue. Here are some of the most important layers (Fig.07). The background was just a random texture with some contrast correction and a rendered lighting effects filter. To achieve this glow effect you can go to Select > Colour Range and then use the Gaussian Blur filter. I also did this with the eyes of the Sentinel, too. The Ambient Occlusion layer was also very important to give the image more depth (Fig.08 - final).
Fig. 08 - Final Image
Thanks for your time and special thanks go to Okazaky and Zom-B! Thank you!