Gensou no Idea is the third VN from 3rdEye, a company specializing in chuunige. When I originally played this game, I was a bit more perverse, personality-wise, and as a result, I treated this VN badly, as one of my pet-peeves is dual-perspective VNs. I generally prefer for there to be only one protagonist, and my reaction to this game was colored badly by that.
First, I'll introduce the protagonists.
The first protagonist is Minase Yuuma, an optimistic young man who is nonetheless grounded firmly in reality. There isn't a scrap of malice in this kid, but he is not an innocent or unaware of the nature of the world he lives in... he simply has a very firm philosophy on life, as the result of being raised by a rather... strong personality. Yuuma is a 'cleaner', specializing in the removal of corpses and the cleaning of homes that have been contaminated by them. He takes pride in his work, and he is one of the few optimist protagonists I actually like.
The second protagonist is Akashi, an Idea (the term that refers to beings from Utopia that roughly conform to human legends) who possesses control over fire. His emotions are weak in most areas, partly because he isn't human, partly because he is missing a big chunk of memories. However, he possesses a driving urge to recover his memories and destroy the 'Phantom' who brought ruin to his life. He has a strong interest in humans and believes firmly that he is good at mimicking them, but he is... not very good at it, lol.
Now for the heroines... strictly speaking, there are no separate heroine paths in this game. This game is, like Sorcery Jokers, essentially a kinetic novel where you choose which protagonist perspective you see first sometimes. There are epilogues for each heroine, but they are pretty short and to the point.
The first Yuuma heroine is Naru. Naru is a fortune-teller with a bad case of chuunibyou and an inherent optimism that matches Yuuma's own. She is very prideful and has a tendency to lose her cool rather easily.
The second Yuuma heroine is Rinon. Rinon is an idol and an Idea that Yuuma follows obsessively. She is arrogant, possessive, and violent. However, once she falls for him she is... passionate and loyal. I really, really liked her epilogue, and I almost fell out of my chair laughing at its end.
The third Yuuma heroine is Kokoro. Kokoro is your classic 'emotionless heroine', showing little reaction to most stimuli.
The first Akashi heroine is Noel. Noel is a possessive, jealous Idea woman whose first priority is Akashi's love, second is Akashi's safety, third is Akashi's happiness, and fourth is Akashi's penis.... do I need to go on? One of her ongoing hobbies is drugging Akashi and having him tortured to find out the identities of women he is cheating on her with (she defines 'cheating' as talking to or being talked to by another woman... or looking at them, touching them, or breathing the same air as them).
The second Akashi heroine is Mitsuki. Mitsuki... has issues. She is very much an introvert, and she has a tendency to keep her distance from others. She does get pretty cute when Akashi manages to make it past her guard, though.
This game is based around a century or two after Bloody Rondo (don't know if this is fully canon or not), seven years after a disaster that nearly destroyed humanity. In this new world, where a large portion of the planet's surface has been submerged and the human population has been greatly reduced, Archive Square, the corporation that has taken charge of the recovery, has become the central power in the world. This is the case across most of the world, but the city this story is based in is one where more than half of the population works for AS.
There are two worlds in this game... one is 'Dystopia' (the name Idea give Earth) and the other 'Utopia' (the word the Idea use for their own world). Idea, beings of immense power from Utopia, have been going back and forth between the worlds for centuries, taking the form of humans on Earth and generally indulging their curiosity and whims as they desire.
This story focuses on two perspectives... Yuuma as he deals with the changes in his situation, and Akashi as he seeks the past. This story has a lot of really good battle scenes, emotional moments, and some seriously interesting hedge philosophy (mostly out of Kyouko and Yuuma, though Akashi contributes sometimes).
On my second playthrough, having gone in with a more open mind than my first, I found the story a great deal more interesting. I won't say it is perfectly paced or that the characters are the best I've ever run into in a chuunige (they aren't), but I honestly enjoyed the ride, from beginning to end. This isn't a VN that is likely to make it into my top fifty, but if you are looking for a good chuunige and have already read the more famous names, this is an excellent choice.