On here he remains underrated. Abilitywise, he should not be world class, but he approaches it anyway because he has become so complete. Assured technique, fairly press resistant, good passer. Not spectacular but good enough that he can pick a penetrative pass in the final third.
And then there's the stuff he's learned over the years. Gets around well, always offering himself to solve problems for team mates, gets the ball forward well. Does very well in maintaining intensity of play both on and off the ball, and has the leadership to cajole his team mates into doing the same. And defensively he's top notch, whether it is pressing high up the pitch, supporting full backs or sitting deep.
He's a very complete midfielder. The fact that he is as comfortable box to box as he is in the holding role is a testament to that.
I actually think Gary Neville is not a bad comparison if you considered him borderline world class. No stand out qualities that should make him world class really but being good to very good at everything, the sum of his parts amounted to something that unimpressively approaches world class.
Like Neville, I expect that Henderson will drop off a cliff when his legs go.