One thing that irks me with every simulation tech I have used so far: Most of the time I want to emulate the movement of something from the real world, as closely as I can. And most of the time it's endless fiddling with somewhat abstract parameters to achieve the realistic movement I know from the physical object.
It really should be the other way around. Let me make my object, define it's size and weight and then let me choose from fine-tuned, well-tested presets. That's water! Or milk. Or sand. And then offer an advanced mode where I can fiddle around with advection and all the stuff 'under the hood'.
But really, let me express my artistic vision through my everyday-knowledge of the real world. I don't want to study particle physics for any simple sim I do.