Update on Metroid Prime 4: Development restart. Retro Studios + Tanabe now working on it

[Nuvendil]

Pavolink said:

Btw, what could cause a development reboot? I find that decision pretty drastic.

If it was just graphics, they could focus on it, but this sounds more than that. Bad fundamentals of the game? Engine not working? Full of bugs?

My guess is fundamental design.  Metroid Prime is a very particular kind of beast.  The new dev might have struggled with it, making it too linear, too story driven, too action oriented, or too obtuse.  All these things spring to mind.