Last week I test drove the M5, E63, R8 4.2, and 991S back to back.
Honestly, I liked all four of them. For me I would prefer the Porsche because I don't need 4 seats. The E63 was noticeably slower than the M5. The R8 is a lot of fun and sounds so good but the Porsche just runs away from it.
I don't think BMW messed up but I do think they need to get on board with making their cars lighter. Audi, Porsche, and Mercedes are all focusing on that now.