Adam,
In simplistic technical terms, we are usually talking about earthmoving, as most courses don't have the the luxury of building water features you use as an example.
As far as earthmoving goes, I think there are two simple tricks to making it look natural. The first is to reflect the landscape. If in a gently rolling area, use gently rolling features. A few years ago, an architect writing here said he used a guide of not having steeper slopes that more than doubled (i.e. if natural grade is 4%, then any earth featuer you build should not exceed 8% slopes) the natural grade of a particular area.
Probably not a bad idea for going natural, even if you cheat and to to triple once in a while. I think the real trick is to keep the skylines of the earth forms no more than double the natural grade, ie no himalaya mountain tops in otherwise flat ground.
The second is to watch the tie ins. Architects tend to build 25-33% mounds/earthforms that end abruptly at a rather flat natural grade, rather than transition from 25%, to 15%, to 10%, etc. I think one of the oldies wrote about this similarly, but I call it tying in the slope. The problem sometimes is that this takes a lot of room, and when you tie it in to a cart path, that may put the cart path too far out of play to be useful. Also, real estate boundaries also confine the tie ins sometimes.
So sometimes there is a compromise in order, as in all design.