I, for one, find 3d6 to be a much better method for RPG skill checks. Somehow a complete incompetent can critically hit a master 1 out of every 20 swings and a master can critically miss an incompetent at the same rate in systems that use a d20. 3d6 gives you a nice curve where normal events are common and exceptional events are more exceptional. Rolling three ones in GURPS just feels so much more satisfying.
There's an issue too where the flat d20 system makes the AC and +hit scaling really off in my view.
If you go from only getting hit on 17+ to only hit on 18+ then you are reducing your incoming hits by 25%, and the scaling only gets even more skewed from there. Whereas on a barely armoured wizard, going from being hit on an 8+ or 9+ barely makes any difference.
In some sense it encourages specialism but on the other hand it doesn't sit well with me. Having extremes less likely would also help with this since you'd be cutting out a smaller chunk of the curve each time.
https://boardgamegeek.com/thread/1859998/designing-dice-do-n...