To be blunt, Ryouko is a sub-heroine, so there really isn't much to say about her. Her path quality is lower, the details are less involved, and the drama is so mild you almost have to ask yourself if it even exists. Despite this, she is a fairly cute character, and she does fill the 'adorable kouhai' slot nicely.
This path, in terms of quality and nature, is something of a hybrid of Shizuku's and Reina's. Similar to Reina's, it is an osananajimi's path, with the assumption of past relationships and the reliance on them to form the protagonist-heroine dynamic. However, at the same time, it also possesses the kind of depth of introduction and character development that made Shizuku's path so satisfying overall. It makes sense that you have to have played at least one of the previous paths to access this one, when you consider the quality of this path.
That said, I think a lot of you will be a bit shocked at how their romantic relationship gets started, so feel free to look forward to it.
A few comments. This path and Ouka's are set on a story branch that is separate from the previous three, which has a slightly more intense focus on the fantasy element than was the norm in the main story of the other branch. Because of this, the two paths that follow feel a bit less like charage paths, which should be satisfying for those who prefer the more intense experience that came from Tasogare no Sinsemilla, though it still doesn't reach those heights.
Ouka (True Path)
Ouka is... a complex character. She has a number of roles: ghost, advisor, armchair detective, confidante... but in the end, she is the true heroine. Ouka's path is... the most complex and 'complete' of all the paths, with the most powerful emotional impact.
The first half of Ouka's path alone is as strong as Shizuku's or Shione's paths as a whole, and the second half (started from the title screen) is easily the densest drama in the entire VN. That said, all of the drama is intensely personal. There is no element of 'save the world' or 'cut the ties of an ancient, dark fate'. Rather, this is a romantic story, focusing on the relationship between two people who are as close as it is possible for two beings to be.
All the aspects of the protagonist's ability (including what is only hinted at in the others) is revealed. In addition, the hidden truth about Ouka is revealed, which is never even really touched upon in the other paths (deliberately). This is the only route I cried for, and it is worth playing this VN solely for this path...
First, a few things I left out above. Ouka's route has two endings. One is an Tsukihime/Akiha-style 'normal' ending and the other a 'true good' ending.
Despite the fact that I raved about Ouka's path above, I do have to say that if this had just been a normal romance between normal people, I probably wouldn't have been so into it. I'm a fantasy freak, and I love out of this world romances.
At the same time, I felt that the writer's indulgence in 'the protagonist gives up his abilities' trope of Japanese fantasy fiction was a bit annoying. I generally dislike the way the Japanese tend to try to get rid of anything outstanding about the characters in fantasy stories.
A major flaw of the story is that there is no ending where Michitaka uses his ability as part of a career (it would be really easy to do so, and it would be interesting as an ending), and most of the heroine endings other than Ouka's left behind a definite feeling of incompleteness, despite the H-filled after-story 'fragments' you can access from the flow chart.
A major advantage to the way they construct the flow chart is that you can access the extra scenes along the way that enhance the story... or you can just live with the characters' casual mention of the events that happen in those stories. Little things like the protagonist's first meeting with his best friend's little sister, and certain people's reactions to Ouka are in such scenes... so it can be a good idea to look at them. At the same time, this is a VN of respectable length, so you might feel that it is better not to do so, due to your own personal time constraints.
On the whole, this is a good VN for those who like fantasy, and - while this is no Tasogare no Sinsemilla despite having the same writer - it is still a well-written narrative.