EDIT: Ops, I wasn't sure if this was a bug report or a feature request - duplicate post.
When merging / voxelizing in perfect 90degrees angles then the surface created is perfect; however, just tilting the object a tiny bit in an axis creates very noisy and undesired surfaces.
To demonstrate the problem, here is an image comparing a 90deg merge and a tilted merge:
The way that I'm working right now is by making everything in 90deg angles then taking it into surface mode to distort it in different angles.
It is a very cumbersome way of working and very limiting to what is possible to make.
Perhaps you could look into it ?