"He's not the kind of player you can talk about strengths because he has many things he can give to us."
The Ukrainian international was out of contract with the German club, but transfer details have not yet been revealed.
"The Liverpool fans are world famous, and though this was not the only reason I decided to join this club," he said. "It was certainly one of the main reasons. I can't wait to play at Anfield in a red shirt."