This is a great entry and there is a lot of good stuff in here.
The little beasties in the sea is a nice touch. The city blow outs are cool.
I think you did a great job with the mountains and overall feel.
If there is one thing that snagged my eye at first glance it would be the deserts. I'm not sure how they were made but they give me a different feel from the other elements.
If that's the purpose then great but it almost looks as if they were generated and then merged in with the rest. If you had the energy you might just go over them by hand and smooth them or something.
Then again that's the only thing I would probably do with it and I'm just a person looking on and not the greatest around here so I might be entirely out to lunch
Either way you have a contender. Good job!