1. The water lines.. There' s alot. I recommend when you do those smooth em' out. I have no clue how to do that in Gimp but in PS its Select-Modify-smooth (insert amount of numbers) I'm sorry but I get easily frustrated at perfectly straight water lines. I recommend like.. 4-9 that continously go further out and maybe some distortion here and there. And a bit erased here and there also.
But, thats just my one cent! Good job so far.