Just got finished with the demo, and I really loved it! Definitely a little upset to hear that I'll have to abandon this team for the full release but that's totally understandable for all you have planned and I'm excited for when that gets completed.
The sprites, music, and maps are all really impressive and tastefully done. I think all of the puzzles were really well thought out, too, and really fun to solve. I really liked the hidden grotto implementation here. Fun little exploit I noticed; if your bag is full when you try to collect a shard, the grotto will continue to generate a different colored shard every time you interact with it. When I wanted to get a specific color shard so I could get a certain tutor move, I would make sure my bag was full and to also be carrying only the color shard I was looking for so I could only collect that kind. Similarly, I loved how many hidden items there were all around the region and how they were generally hinted at by the map design so it felt like it was really rewarding to pay close attention.
I will echo that the level curve could use some tweaks, as there were several spots where despite having battled every trainer, I was vastly outleveled by other trainers who could OHKO most of my party making it hard to win without going to grind or relying on good RNG. Notably, I play with battles on Set, and my friend who is also playing is not having as much of this issue on Shift although she also spends some time grinding against wild Pokemon with fast forward on, but is still noticing notable level spikes. I think some of the challenge is exacerbated by the abnormally high evolution level of many Pokemon in the Unova dex (in my party Litwick to Lampent at 41, Joltik to Galvantula at 36, and I abandoned my Vullaby after realizing it doesn't evolve until 54) which means I had first or second stage Pokemon up until around the 5th/6th gym. I do like the challenge though with trainers having Pokemon with movesets that cover their weaknesses and that many have held items, so it does require more strategy without being too overbearing. I'm not sure if there was a specific reason for not allowing the Exp. Share to be obtainable until after the 4th badge, but I think it would've been a huge help to my party to be available earlier, and to maybe have its location be a bit more telegraphed.
In terms of progression, I somehow managed to find and defeat the 6th gym before the 5th, and went all the way to the end of the sewers before realizing I couldn't use Strength yet and had to visit the towns I'd been to before to find it. I'm not sure if there was a moment in the plot where I didn't notice that the 5th gym became accessible, but my friend who is playing also had this happen. I have no problem with facing the gyms out of order, but this didn't feel like it was completely intended.
Some smaller issues I faced were some enemy Pokemon (like Scraggy and Liepard) had Thief in their moveset, which permanently takes my Pokemon's held item, and it felt pretty bad to lose my Eviolite and Scope Lens that way during my run. It would be nice if it could either be returned at the end of the battle or removed from enemy Pokemon's movesets. I really like the sideway stairs for map design and aesthetics, by I found that the pause after going up or down interrupted the flow of movement a lot as the camera worked to catch up. Could this be sped up at all? The last thing is more of a general Pokemon/Gen 2 thing, but a lot of enemy Pokemon carry confusion and sleep inducing moves which can be frustrating to be up against with the 50% self-damage rate of confusion and up to 5 turns of sleep present in Gen 2. I wonder if those couldn't be updated to gen VIII standards (33% chance of self-damage and a max of 3 turns sleeping)?
Really great hack and I'm looking forward to picking it up again in the future! (: