Right so i think i should give my 2 cents
first off, this is brilliant as a fan of gen 4 myself the recognizeable and fitting music was phenomenal, the region was well designed and everything seemed to function correctly aside from a few collision bugs (invisible nothing blocking my path for example)
i will however say that the game needs some serious balancing issues in terms of levels. enemies were so much higher levelled than wild pokemon that it was almost a chore to raise new team members and when it came to big fights like gym leaders i found myself falling back on my high levelled pokes and not getting a chance to use my lower levelled ones. also while i appreciate the last gym being your rival and having no specific theme he is a bit too difficult tbh (typhlosion with fire gem eruption wouldve been murder if not for chandelure) i also had to grind to level 50 on victory road just to avoid random encounters with repels and even then i struggled a bit with the elite 4
you also don't get nearly enough cash, i was running out of repels, potions and revives with very little cash if any to restock making some fights that much harder. also adding a PC somewhere in the first town to avoid having to go to mountain town and back when replacing pokemon would be a nice touch
all in all it's a solid game for something developed by a single person i'd say its a great effort, better than some of the fan games out there that have entire teams behind them. just a little rough around the edges is all.
Good luck perfecting it and i hope you do well in the future