I wasn't entirely sure what to expect when I downloaded this, but it sounded undeniably unique--so I gave it a try.
And man, I'm glad I did! It honestly pulled me in a lot, moreso than most VNs I've played in awhile. I think maybe it's because it felt very visceral and straightforward--no longwinded introduction or huge text blocks, and with emotions/narrative that hit me in the face rather than feeling forced or drawn-out.
So, warning, rambly review and thoughts:
My first impression was how much I liked the GUI and aesthetic; even though the menus and buttons are still recognizably close to the Ren'Py template, the choice of fonts, style, and VHS-themed word changes really fit--enough customization to feel like real thought and mood/atmosphere consideration were put in. It reminded me a decent amount of Hotline Miami 2, incidentally...any inspiration there, or just coincidental?
When I got into the story, I was kept guessing at where things would lead, in particular the choices. I got really attached to Heiko quickly--like someone else said, he's very sympathetic, even if he's an asshole; maybe because his inner justifications for doing things are applicable to a lot of other situations/things we do. I felt dragged down with him, despite the minimal backstory we have--actually, maybe because of it, since it really lets your mind wander and fill in the blanks, and sometimes that's much more powerful than explaining everything in detail. In this case, it definitely worked.
The tankheadedness took some getting used to, but as time went on I started to rather like it, especially contrasted with humans...I had some theories spiraling in my head about what the differences were, which was neat. For not having any expressions, the body language in sprites and CGs for the tankheaded characters was well done, and actually a refreshing change from just reading a character's emotions through their face. In the same way that a movie is sometimes better in black-and-white than in color, I also felt like a lot of the game was enhanced by the main characters not having human facial features. For some reason, I really don't think I would have connected with them as much if they had.
Sound effects were good, not too many but fit well. I also liked the music choices (with the exception of the one vocal track that played somewhere during the game, vocals are a bit hard to listen to while trying to focus on reading), so well done in both regards there!
Overall, it seemed like the clear product of love and effort, and I found it genuinely moving. I've been writing about drug abuse both in a literal and allegorical sense recently, and maybe for that reason I really connected with the story. I don't think typing up an analysis here would do it justice, since I found it more resonant in the Lynch/Jodorowsky/Serial Experiments Lain type way, where you sort of understand things with your gut or in a visceral sense rather than a logical one.
I hope you continue to make more games in the future, I'll most certainly give them a try!