Paladin in my group got a Vorpal Sword at level 14 or so. He failed to roll a natural twenty for three levels, and was despairing of it. Then promptly decapitated three Goristos in a row. Damn that thing! Damn it to heck!
In fairness though, it's a fun weapon, and definitely memorable.
Yeah the Paladin in my game didn't roll a 20 for a while, then he rolled a 20 against a CR18 demon with over 300hp first round before it could even act, and then again against a CR18 medusa sorcerer who also had over 300hp. He was foresight so he has a chance of rolling a 20 in every fight pretty much.
You're right though it's been fun and memorable, but I won't give one out again!