Season 5 is mildly disappointing, Season 4 was a strong season, season 5 failed to properly follow up on what was set up or properly build on it. It picks up after the events of Season 4, the first 3 episodes do deal with Mo Fan and the demon element, after this is resolved and these episodes end, we get into the main story of Season 5. For some reason he is sent to Song City to recover (because apparently he can't just go back home and return to the academy) it is inferred that he was weakened, although he's clearly not, and basically the story needshim to be there for the sake of the plot, which involves a mystical snake, has no real baring on anything else, and is basically just side story filler.

The story arc itself is fine, it's a little convoluted, but it is all wrapped up before the end of the season.
The problem is when you get to the last episode, which feels like the start of a new story and feels like the start of where the true story should have been, you can't help but feel that you want more of that, and could have done with less of the snake.
I've not read the story this is based off, but even I can tell that the focus is all wrong, this is a series that has a story that it wants to tell, normally you would focus on the main story, you wouldn't tease your main story and leave it for the next season, because you may not get the next season made.