He's an absolute genius. I have always preferred Modric, but different types of players. He had a rocky start to his Real Madrid career, and can still be suspect against pace on transitions, but he's so calm and composed, always knows the right pass to play in possession, always executes it well and with perfect precision and accuracy - very rarely is there a missed pass or a mistake. Many of his passes are short too and he's economical with the long diagonals, and only plays the switch of play when it's definitely advantageous.
The guy just oozes class and it has been a pleasure (to a point) to watch him (and Modric) in that Real Madrid midfield, even if I wanted them to win absolutely fuck all as I prefer Barca. He's the type of player that all young midfielders should be told to study and watch - watch his movements, how he scans all around the pitch to get a picture of the play and be 2-3 steps ahead. How he's ready to keep the ball moving and the game ticking over. The guy controls games and does it in a manner that seems so effortless.
Xavi, Iniesta, Busquets, Kroos, Modric, Pirlo, Redondo, Scholes - we have seen some fantastic tempo-setting central midfielders in this century. Putting on my neutral hat I would like to see Kroos continue as he has plenty to offer still. However, he's clearly one of those guys who wants to retire while he's on top and not taint his legacy (unlike some...) and that is a very very underrated quality in a person.