Hi Hafidz,
A couple of things to think about:
1. Maybe a bit tighter editing. There's a couple of shots that probably should have been cut - subject partly out of the frame, too much jiggling. It's tough editing your own footage. Try being a bit more brutal on yourself.
2. Youtube compression spoils some sections. Always bad at areas with a lot of blue water. Look at a better video service like Vimeo.
3. It's a personal choice but I found some of your colour correction a bit too much. The reds and browns look at bit overdone. But some people like that look. I don't like it because that's not what the human eye sees underwater.
4. Little bit frustrating when someone is saying something to the camera in the first section but you can't hear them. Sort of looks like an old silent movie. If the sound didn't capture well, throw on a subtitle. What did he say?
5. Next time, rather than just stringing together a bunch of good clips, have a think about the story that you want to tell. Then edit to that story.
Regards
Peter