The whole waking up in a novel and knowing the plot actually had no real impact. The story would be perfectly fine without that. Nothing about the plot hinged on the MC being a transmigrator. That whole bit was a bit awkwardly explained away.
There are some parts of the story that left me confused with questions that never get answered, but the core of things had an appropriate and complete conclusion.
The core of the story being the relationship between the main characters.
Their relationship is the very typical miscommunication, coming to terms with feelings, misunderstanding, being dense type of relationship. It's a little annoying at times.
Where this series excels is the unique setting and use of non-humans. If this were in a modern college setting, I'd be rating it lower. The world building makes up for some of my issues with the story itself.
So many things left me hanging though...
-- wtf is up with that life tree's behavior at the end?? A bit unexpected and seemed kind of significant since it fundamentally changed my understanding of the existence of the winged race
-- what happened to the religious order after the climax??
-- why was that boy child Sehn involved at all? I don't get why he was wanted by the demon lord
-- how was Alaister born??
-- what happened to Lich and Erich in the demon world? What's Erich going to do?
Did they die or something I'm not clear on that
Oly spouting "I'm in it for the money" was sudden and weird
-- if the winged people have no gender, then...huh?
-- the change with the former FL was unexplained... In fact the whole novel plot aspect was not explained. Is it actually a novel or is it reality and his modern life just a previous life? Both premises were used
Isn't Alaister a fugitive now? Shouldn't he hide his identity when they're in town?
Yeah, a lot of things bugged me by the end. The above is not even all of it haha...
In short:
Don't try to think about the story logically because you're gonna have a bad time. Just enjoy the evolution the main characters's relationship and the interesting world.