I am kinda on the opposite front actually.
I didn't like the ending. Maybe its because I really haven't read the rest of the Liarsoft saga and whatnot, but I felt that the entire last chapter (including the "grand twist") was so asspully that it was insane. I won't get into the specific details here, but I felt that it was severely lacking in clarity and cohesiveness for a game that has a bloody encyclopaedia in it.
Mild Spoilers
The fights were... bad and mainly composed of Tesla just beating the shit out of everyone while endlessly monologuing them about their failures. They are over the top, but not in a fun silly way like Fortissimo, but more in a "our character does what he feels like" kind of over the top, where Tesla just perfectly counters everyone without ever being even remotely threatened by anything they do.
Tesla actually kind of reminds me of Tatsuya from Mahouka in that respect, really. A nonsensically overpowered character, who you need to routinely de-power to maintain any sort of tension in the fights themselves.
However, I did really like the side-characters and the way they built the character relationship between Neon and Tesla. The art was great and the soundtrack was okay. Neither did it really drag on, something which I typically find somewhat of a problem in these episodic-type stories. However, the porn was incredibly hamfisted and this is one of those VN's which I think would be significantly improved with the removal of the porn scenes.
So in general, I liked Gahkthun. It was very flawed (for me personally), but I still liked it. Which says a lot about how well the character interactions were done. Hopefully the fandisc will be more of that and less of... everything else.