In the first place, there are some requirements for a song to make an alternate map.
The song should have some drive with consistent background drums that allow you to keep mixing 2/1, 1/1 (mostly for melody) and 1/2 (mostly drum or instrumental fillers) at an effective bpm of ~240 and up.
What can be said about val0108 maps additionally is that readability is a very big concern and mostly achieved through usage of symmetry and consequent avoidance of overlaps while still representing the intensity through varying spacing choices, mostly between sliders. Spacing between consecutive circles is kept constant religiously within a pattern and often even beyond that.
Also very important: Unlike in more modern mapping there are pretty much no individual jumps to represent the music on a more microscopic level, e.g. patterns where you need to perform a jump to the third note of a triple.
You can compare the Insane and Milan's diff in
this mapset. In terms of ease of reading, predictability and as a result maybe also enjoyment, Milan's difficulty is much more comfortable to play because there is no attempt to create additional emphasis on most sliderheads through spliting up the notes of the triple unevenly.
What creates reading issues for most players in the Insane is that the triples are split differently depending on context: You can have 1 note jumping to 2 stacked notes and 2 stacked notes jumping to 1 note, partially even in very close succession without clear cues in the music. As a result it requires a lot of attention to play correctly and makes the map - combined with the high speed - rather stressful to play if you're actually trying to FC it.
While the style used in the Insane can be interesting to play, it is (in my opinion) much more enjoyable in maps that sport a lower speed and slider velocity in general so that those microjumps and a focus on music representation through cursor movement become the main gimmick of the map. An example would be the splitting of triples in the middle section of
this map which feels very classy and easy to understand as it is used in a consistent and predictable way and not layered with other difficulties.
So all in all, readability, readability, readability.