1. There is a bug in the editor. It appears that you do not clear your rivers between one world generation and another. To reproduce, just click "Generate" in the editor a few times - rivers will be everywhere, even on the ocean tiles

2. I have a little suggestion. It looks like the world generation is rather simple at the moment - you seem to use some kind of noise, an then you map the land elevation to the noise value at the relevant point. While being efficient, this leads to very predictable landscape - flat terrain by the ocean and hills/mountains in the middle of the landmass. You might consider doing some kind of simplified plate tectonics simulation to spice it up.