I personally don't like him that much. As someone has said, he's not exactly the type of player Dortmund needs right now. They already have Lewandowski, Aubameyang and Reus to bang goals for them. For around 30M, they could have gone for Hamsik. That's an extra 5M, but it would be well worth it and he would have suited them perfectly. Also, another good candidate in my opinion would have been Valbuena. He's much cheaper (around 15M), has a decent amount of experience, knows how to find teammates very well. And they would have spare 10M to strengthen other parts of the team.
Lewandowski
Valbuena - Reus - Kuba
Pretty solid in my opinion.