What kind of player is he?
He seems a pretty complete defender. Really good in the air, physically really strong and surprisingly swift for a player his size. He's not a Pique when it comes to build up play, but he's been improving quickly, as he's no numpty with the ball at his feet.
He never used to really 'play football' but just defend and pass to the nearest player, but he's visibly improved, even dribbling and generally just being better when it comes to contributing to the build up. He's one of the ( Bryan Ruiz being the other ) main reasons Twente won the league, an absolute wall at the back.
I remember reading about him that this is his third year at football club, so he's really inexperienced, but often praised for being an unbelievably quick learner, capable of doing a lot. Supposedly really good, but obviously a risk. I think he's valued at about 7m though, so he's rather cheap.
I think there are people who seen more of him though, as I haven't watched Twente week in week out.