Just finished up my playthrough and thought I'd drop a couple of my thoughts, or a mini review. First off, I absolutely love how the dialogue/text was written, truly felt very immersive and gave it a 'high quality' feeling as well as a mature tone. The graphics as well as the slightly modified HGSS music is absolutely sick, as they did feel nostalgic, but fresh at the same time. I think the hallmark of a good fangame is when you actually feel a range for the characters despite having not been in their shoes.
If I had to be very honest about what I didn't enjoy, well, it was the certain scenarios which hinted at what's to come in your next game, as 'The first adventure' is a prequel. It did feel a little too jarring for my personal liking, and while I know you weren't pandering towards nostalgia, one can't help but find Kanto to be very nostalgic. I also wish we had some emphasis on Agatha and how she switched up towards being a ghost trainer.
That aside, I did thoroughly enjoy myself playing this fangame. I love how you took what was once a mere intial concept by gamefreak and built it into one helluva game with a healthy amount of difficulty. Never have I been more careful with spending money in any Pokémon game till now. Heck, I even lost on purpose at times because healing cost way too much, hahaha.
Good luck with what's to come!