I had a sci-fi plot sketched out in my head, I had Codex give a whack at it. It was "ok" - not the worst content I've ever read, not the best. It was "sufficient."
My take? It was passable. Over the last year I've read quite a bit less because I spend a lot of times looking at screens during the day and periodically get headaches, but I read something like 12-36 books a year depending on the year. Some of the fiction I read is good, others is... well, it's adequate.
From a purely "was it good enough to make money" standpoint, a book written exclusively with codex could probably sell copies. There are a lot of crappy authors out there too.