I know we already have a thread about how "feels like part of a larger narrative" shouldn't be a criticism, but I really think it was a major flaw in an otherwise very good story. It felt like it was written with the assumption that we already knew certain things about the setting and characters - the parts where Hereward explains he was raised by the witches, for instance, or why Mr. Fitz was able to pass through the barrier, seemed like they were supposed to be Dramatic Reveals™, but without any pre-existing background for them they just fell flat to me. Especially the latter - the fact that Mr. Fitz technically qualifies as a pregnant woman has absolutely no bearing on the rest of the story except as a convenient excuse for not putting in a barrier-breaking scene. In a larger narrative, there probably would have been hints at his nature, and the explanation would have been a very effective "aha!" moment, but as it was it seemed to come out of left field for very little reason.
The witch thing is similar. If we'd known about the history of the setting, and had heard references to the witches as evil, god-killers, etc., then the fact that Hereward was raised by them and that their purpose was good would have been a much more powerful moment. Again, without that background it comes off as somewhat forced exposition instead.
Again, I liked the story, and I think total immersion can be a very effective way to worldbuild if you do it right. But there's a difference between gradually revealing the world by example as you go along, and just pretending everyone already knows what you're talking about. They look the same, but the effect is very different.