This was overall a pretty nifty game. Just got a few thoughts for it:
It's not terribly clear on the map screen that the alternative paths are no longer selectable. Darkening the unselectable icons or changing their appearance in some way might help with that.
It ultimately didn't really feel like the !, !! and !!! icons really meant much of anything, as occasionally lower-tier enemies were a lot tougher than higher tier ones.
Aside all that, the interface is great. Had no real issues piecing my islands together, shopping, really much of anything. Solid effort all round.