This is a review for those who've watched the first two seasons of hell girl, if you haven't watched hellgirl by now you need to start with season 1.
Everything about Mitsuganae is mediocre compared to the first two seasons. While the first season wasn't perfect by a long shot and many critics had lots of issues with it, Mitsuganae (the third season) is a disaster compared to it. With season 2 being the best.
The problem is that the third season has the same problems as the first, except this time it's obvious the writers ran out of ideas. The repetitive plot / revenge structure with an episodic nature comes to dominate mitsuganae once again with a "main plot" that is just so poorly written into the vast 26 episodes that the plot comes out nonsensical.
Most of the 26 episodes of the show is filled with filler material. There are maybe 6 episodes total that have anything to do with the main plot and the rest can be skipped. The 'new plot' they came up with for season 3 is just hackneyed. The plot is basically hell girl possesses human girl and hell girl has to save the girl she possesses. The problem here is that hell girls finale in season 2 was having hell girl be released from her role as hell girl and finally getting to die. So the plot begins with a deus ex machina, which is just amateur level writing. They never came up with a believable reason for why she is back.
The producers also went and made huge radical changes to the characters and cast so it throws off the FEEL of the characters they established in the hell girl universe.
The plot involving possession is just so forced and convoluted that it turns off the long time fan. Each episode of mitsuganae feels rushed and it feels rushed because the characters and their motives were not written well at all. The main problem with mitsuganae is the characters in each episode take revenge for the dumbest and most unbelievable reasons. Hell girl and mitsuganae relies on characters in each episode beside the main cast never appearing again. So the fact that the characters are not believable goes a long way to making the whole show a tired excercise of you trying to tolerate its badness to find the good episodes that make any kind of sense instead of wasting your time.
If you're a hell girl fan watch season 1 and 2 and skip 3 in order for you to not end up with a bitter aftertaste in your mouth.