The best midfielder of this century for me and certainly one of the most complete midfielder of all time.
I have him above other greats of this era like Xavi, Pirlo, Iniesta, Scholes, etc. because he has more dimensions to his game. He can do what these players did when it comes to press resistance, controlling games, passing, vision, creativity, etc. (this is arguable of course but the difference in quality would remain marginal), but he's on a completely different level when it comes to athleticism. His amazing speed and insane cardio, precisely, have allowed him to be very comfortable carrying the ball forward, effortlessly run past players and be a great defensive asset, all the way through extra-time if needed. He has done this his whole career and can still do it at 36-37. Xavi was good defensively, essentially thanks to an excellent spatial awareness and positioning, but he couldn't dribble. Iniesta was a fantastic dribbler, especially in tight spaces, but he was poor defensively.
This mix of technical brilliance and elite athleticism is almost unheard of for CM's and that's what sets him apart. It also makes him adaptable to any tactical systems and effective in any types of games, be they well-structured or disjointed ones where the tactic goes out the window.
His longevity is also unmatched amongst midfielders, and personally, I find him more aesthetically pleasing than the names I mentionned, except maybe for Iniesta.
The only midfielders from this century I could consider better than Modric would be Zidane and Ronaldinho, but they weren't CM's and Ronaldinho didn't stay at the top very long.