My entire experience has been: good management + talented developers = success, and bad management or untalented developers and it fails, but it really has nothing to do with the methodology in play. I've seen (and been part of) hard core agile teams burning to the ground, and teams with no methodology be wildly successful. (And vice versa)
Agile bothers me because it generally aims to commoditize developers, and yet the best places and teams I've worked on always were they opposite: it was about finding the best way for each individual to work, and designing processes around the rhythms around whatever industry they were working in, rather than assuming everything should fit into 2 week sprints.