I think the best way to describe him is that he's very similar to Koscielny but has a hint of Mertesacker in him, he's quick and covers well, but he's quite smart too, I don't think he's a ball playing defender though, and he's a good athlete. I haven't seen much of him, but I have seen him play for Olympiakos quite a few times and his perfromances for Greece at the World Cup always seemed to stand out for me. Don't take what I say as gospel though, as I didn't really pay much attention to his individual performances when watching games with him involved, but it would always get to a point where I'd be watching and think "That guy's been really good." and it's always been Manolas.
Obviously we could sign him and he turns out to be Squillvestre, but, we'll see.