Personally I enjoy having natural 1s and 20s being auto fails and successes on Saving Throws. Because of 5e's bounded accuracy, it rarely actually matters, but when it does it is so incredible exciting (or crushing). Also, it helps out at higher levels where many Saves don't keep pace with enemy DCs. I remember playing a pvp-esque one-shot where my 8-Int Barbarian (and the entire party) was Psychic Screamed by a caster with a DC 20 ST. Psychic Scream stuns those who fail the saving throw, is not concentration, and lasts until you successfully make the save....which in my barbarian's case was literally impossible with his -1 bonus.
In addition, Saves are reactive to avoid an effect instead of proactive to attempt something, so natural 20 = auto success avoids the "you roll a nat 20 on Atheletics to jump over the moon" problem. Why shouldn't a character having a 5% chance at avoiding a Dominate Person or Fireball or even Sacred Flame cast by a high level caster? Is that really more unbelievable than a level 1, 8-str wizard rolling a nat 20 to hit a super armored, AC ~24+ enemy?
