From a personal viewpoint, your rivers seem awfully smooth and of even thickness.
Especially for a good sized island nation.

I'd think they should be of slightly varied thickness to differentiate stronger currents, larger and smaller rivers, etc, as well as having river deltas at their mouths.

Though I'm not trying to come off harshly, you seem to be looking for anything people consider uncommon to a map.
If I came off as abrasive, I apologize.