I would usually be sad to see another original RPG go 5e compatible but Neuroshima was infamously poorly designed ruleset, possibly worse than Shadowrun. I probably won't be running it, but may steal statblocks for my 5e game if I need weird stuff again.
The issue with the rolls arises when you have modifiers (like skills), which are in percentage, so you need to sum them up and then cover result and apply it to the roll. Oh and also, you apply Difficulty Levels to your relevant attribute, which are really weird. Easy is -2, Average is 0, Problematic is -2, but then Hard is -5, Damn Hard is -11 and Lucky is -15
So in theory your action should be "roll 3d20, see if you have two successes under relevant attribute" but in practice it's "add DL to your attribute. Sum up all the modifiers, then convert the sum to a percentage of 20.Roll 3d20. Apply the number you got to the roll results. If two or more results are equal or lesser than Attribute, you succeed, othertwise you fail".
And THEN you add complex rules for every single minutia thing on top of it. Or lack of rules for things that were deemed to important, because those were relegated to one of many, many expansions.
Oh and in combat you instead roll a d20, and you need 3 different d20's for 3 different phases of combat.
And then you add the poorly organized book, sometimes contradicting itself (eg. you are supposed to fill a questionnaire to explain character's concept and what they do BEFORE rolling dice in order for your attributes)
Dear god in heaven - I'm pretty sure that applying percentages to a d20 violates the geneva convention.
Thanks for the horror story! What a cautionary take in how to destroy an otherwise serviceable core mechanic.