In the Stern's Bridge thread there was a point early on in my coloring experiments that onlookers were calling a watercolor look, and Torstan added this post. As far as a hand drawn look, the use of dark outlines tends to contribute to an illustrated look, IMO. I noticed this first in Ascension's April Challenge WIP. Also worth looking at is Ravell's recent WIP, Greyscale Non-Destructive Experiment. Note how the coasts and rivers jump, versus the forests and mountains. In his first color version he adds a dark outline to the forest, which, also IMO, made it more a part of what he was going for. There are other examples, I'm sure, just take a stroll through Cartographer's Choice Forum looking for hand-drawn or illustrated styles.
Edit- Of course, nothing looks more hand-drawn than drawing by hand, .