The lvl 15 gold mine creep camps drop a lvl 3 perm + lvl 2 p-up, I'd rather use a lvl 1 p-up here since that combination is not standard. Similarly, the lvl 19 creep camps guarding the play gold mines drop a lvl 4 charged + lvl 1 p-up, where you could use a lvl 2 p-up instead.
The gold mines at the border of the map might be too easy to expand to. I see that you've reduced the gold to 10k but with the camp only being lvl 15 and the distance to the starting position very short ... dunno. Additionally, the creeps are pretty far out and attack units that are walking by:
I would push the mines back into the wood and enlarge it if necessary.
Another creep camp that's aggressive are the murlocs/crab behind the goblin merchants:
Help, a crab is following me! (one auto attack and the evil ensnarer gets you)
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The base entries are pretty narrow I think, especially teal's position on the top right. That makes it too easy to defend your line of workers.
Orc can build burrows behind the red, blue and purple gold mine:
Edit: Actually scratch that, it seems to be possible on several maps now. I don't know why I remember this as a problem.
There are areas outside of the playing field where heroes can be safely dropped off to heal:
I assume you don't want that to happen since you've placed pathing blockers in most of those areas.
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Personally, I'm not a friend of boats - especially not when their sole purpose are cheesy backdoor attacks on the expansions. I can see why some people would like to have that challenge in their play though. Guess you'll have to wait and see whether the public accepts it, but I foresee that there will be as many lovers as there will be haters.
The graphics are very solid. It's a good mix of doodads and it looks warcraftish. I'm not sure about the Felwood leaves terrain, it's quite a contrast to the palm trees and makes everything seem a bit chaotic. Dark Grass is okay, Lumpy Grass looks pretty cool and it was a good idea to add that.
The light green shrub doodads in bases look weird when playing UD: