Hey mate, the main reason it got rejected is because it is rough work. You need to spent more time on this and make movements more smooth, make clean transitions, check on how easy to another person to use. Look at other parallax templates, compared to them this one looks really unfinished.
It is a bit hard to describe in worlds but to make some points:
- Bad parallax - yes you made things move around but there is no feeling of motion.
- No story - I guess slideshow suppose to tell some story, here I see just pictures change each other.
- Low on details - Right now it is random lines with pictures split in circles. You should think in categories like this is big object, this is small object and this is some debris. You can see it in other projects, there is pictures, lines and particles.
You need to polish this one. Wish you luck with that. And let me remind that there is a lot of parallax out there so the competition is pretty serious you need to make it top notch. Best thing to do right now is to watch other videos with parallax to understand the difference and use it to perfect your template.