I'll start by saying that this series will definitely not be everyone's cup of tea. Fukashigi Philia is very fast paced and will probably be confusing for some by the end of it. Some parts of it might feel a bit contrived as well and the truth about Tasuku's past might be disturbing for some readers.
However, I like these kinds of stories -- it dabbles a bit into horror at some points but isn't especially gory -- so I wasn't set off by what I mentioned above. I've seen stories that ended (perhaps) prematurely and had worse endings (looking at you, Blood Parade).
So, what did I like in particular about this series? Well, all of the main characters are strong in their own ways and they also all have their own faults and weaknesses. Some of them are more apparent than others', but that's okay. The characters are also pretty diverse, but they have a true bond (with the possible exception of a certain character ...) and even if they're rivals over the same guy, they'll stick up for each other no matter what. A lot of series have a problem where the main character is the only one in his group that's actually useful, while the others take the backseat. Not so here. Each character is vital to the group, and their cooperation is necessary for their success.
All of their pasts are intertwined -- only Miisha is spared from being directly involved in the fiasco -- and it's all very tragic. It's also all very disturbing. It can be seen in chapters 14 and 15, so if you have a particular aversion towards incestuous subtexts, murder, torture, and mind control (and creepy eyes), you probably want to avoid this chapter. But this past has very real, very lasting effects on the characters in the present, and it's nice to see it all resolve.
The last chapter, which has yet to be translated, is rather confusing, so I'll have to wait until it's released in order to judge the series resolution properly.