By "American Musical", do you mean a musical with an American composer? I mean, this particular musical is about Europeans for a European production, so I'm not sure why Nunn is such a bad choice. The man did direct three of the longest-running musicals in the world and it's not as if his Night Music was universally panned."
Yes. Although, I'm only judging his work on American-bred musicals from the revivals of NIGHT MUSIC and OKLAHOMA!. OKLAHOMA! was saved by a fascinating performance by Shuler Hensley and some good choreography (I only saw it on B'way), but felt heavy-handed and joyless otherwise. And so did A LITTLE NIGHT MUSIC. Just because his work on the latter show wasn't universally panned doesn't mean that it was a slow-moving, badly lit, ugly bore (again with two saving graces-- Alexander Hanson and Angela Lansbury). It lacked all the bubble and fun that NIGHT MUSIC needs. It isn't TOTALLY Chekhovian. For me, at least.
I just think his work is heavy-handed and joyless, from what I've seen. I still am excited to hear a new Schwartz score.