It depends on the type of game you're running and its an expectation that should be set from the beginning (as is "whether a 20 is a critical skill check at all")

My games tend to be more grounded, so when I have run critical skill checks, they are a success with a reasonable bonus. A critical persuasion check might have the guard believe your phony story but also accidentally let slip some useful info as you're passing through the gates because he's let his guard down.

But in a game where the vibe is more out there and power fantasy-y, heck yeah, let your 20s rewrite reality!