Disclaimer: my opinion and personal playthrough as an individual player blah blah
Obvious grammar issues you already know about, which I know couldn't be helped. I hope it wasn't too difficult to find a person to clean up dialogue, as I know recruitments tend to land flat. The dialogue that was read however wasn't bad! As was mentioned above, Chatot was pretty memorable, and I think I would've liked Chatot becoming more than a translator and possible a more interactable role? Thinking how he could've perched up at the top of the campsite to guide the player and do other things. I think it was also more than just a grammar issue as well, I feel like a lot of sentences could've been cleaned up and executed better as well, and perhaps more interesting cutscenes and movement rather than characters throwing text at each other. Not to mention, some battles kind of happened out of nowhere and a lot of the flavor text and cutscenes felt rushed (WHICH I TOTALLY UNDERSTAND BTW). I also think there was a lot of blank walking space, and I would have appreciated a few more optional landmarks and events. Maybe there's a burrow in one the bigger Torterra trees for example that leads to an optional dungeon?
The reason why I say this is because I actually really love the vibe of this game. The entire game radiates an unbelievable cuteness that I actually really really love, and that's not me just talking about the artstyle alone. I sort of actually liked the characters and who and what they did and are as well as the general vibe of the game. I picked the white haired character and really really liked the detail of borrowing the other person's Pokémon for the adventure, and how they basically now take point. I think this could've been expanded upon and went into more specifics on what each character was and making them more distinct from each other. I couldn't really gauge a personality out of either of them, y'know? I know you mentioned maybe a sentence for each just saying what they did, but it could've been a bit deeper. I'm not asking for an exposition dump though, just a bit more lore I guess!
Gameplay wise, there's actually something quite interesting about picking a team of 5 (as the Pokeballs all seem to have 100% chance of catching, which is a good thing), and then using those to tackle the rest of the game's challenges. The game was much less about training and grinding a team and more of picking one, so people are still having the satisfaction of conquering a battle and that's really cool and it doesn't get annoying! I think I would have preferred a more in-depth game design phase. While the Pokemon selection was good, some Pokemon had a hard time doing anything interesting (Scizor). Perhaps next time look into movesets and learnsets? You can always edit movesets and what Pokémon can do and you could sprinkle in stuff like debuffs and status effects in the wild Pokémon sets to help with bosses, really give the player a lot of cool things to play with rather than a ball of stats + typing for bosses. This also gives you an excuse to give more interesting items and stuff (everything past the Life Orb seemed to be just berries).
Adding to my gameplay critiques, I think there could've been clarity on the objectives. For example, the first time I went into the cave, when I was told to cut down trees for wood I wasn't sure *which* ones I was supposed to be cutting, and I was pressing A on the long wooden pieces rather than the small mini trees, which I thought were decorations. It wasn't obvious which wood chunks were decorations and which ones were objectives. I circled up and down the mountain maybe twice before figuring out the skinny trees were my objectives. Not only that, it didn't tell me how many I needed, until I figured out that there was no limit to how many I needed. For clarity's sake, something like "Our wood is our light source. Grab as many wood as we can, as in the cave, each wood piece will deplete one by one until we run out." or something like that, but add some of the character into it lol. This is important because without that information, people would either learn that they need more wood after running out early, or keep farming for too long because there's no indicator on how much wood is needed.
Overall, I think the thing I think it needs the most is a big paint of polish on everything. Even looking at the book by its cover, there's a lot genuinely charming things about this game and imo it's not solely carried by the artstyle. This was a really unique Jam title and I really liked a lot of things about it. Really great work building this game and it's setting.