Lanzini played for my other half's team, Fluminense for a while, so I saw him in the flesh quite a few times while I was living in Brazil, and even met him wandering in Ipanema once!
I was never all that impressed to be honest. He seemed very lightweight, even in a lightweight league like the Brazilian one. He played, as far as I could tell, mostly 'in the hole'. So he was often the link between midfield and attack, picking it up, turning, maybe beating a man and laying it off.
He didn't quite manage to break into the Fluminense first team, they preferred a 34/35 year-old Deco at the time.
I am not too happy about the signing, its a strange one for me, but hopefully Bilic can get something out of him that was missing. Or maybe he has developed his game in the last couple of years. I will be following this with great interest though