Someone offline said to me the other day that since JYB is voicing the main character, maybe it would have been better to just have had Nero be the protagonist. Thinking about it, adapting DMC4 instead of 3 would have been preferable to me as I was never enamored with the plot of 3 even with all the additions that the manga tried to crowbar in, and 4 is basically the most anime-esque of the games anyway. If you just make some tweaks to adapt it better to screen, such as adding in how Nero got the Devil Bringer and showing more of Nero's relationship with Credo and the Order to emphasise how terrible their betrayal hits, it could have worked quite well IMO.