Ooh, really cool kick off to the challenge Abu! Really nice perspective and great linework, particularly on the underside of the island. Don't go overboard, but it might be worth adding a few more smaller lines to the major mountains in the middle just to keep everything more balanced.

Your city suspended between the mountains is a neat idea...though I certainly wouldn't want to live there looking down that HUGE waterfall!

Great start, and I'm looking forwards to the colour!