1. Fakemon: Why? I understand that the creator wants to be more original, but some fakemon are just... uglier than the "ugly" official pokemon.
2. Bad English and Grammar: I understand that for some of us, English isn't our first language - in which case, hire a translator. But for those who live in countries where English is the official or primary language, there is no excuse for half of the text to be in leet/1337 or to be unprofessional and have random profanity when your plot isn't mature.
3. "Mature" plots: Sex jokes, swearing every 2 lines, internet memes, and pop culture references does not make a mature game. A game is "mature" when it has sufficient character development (yes, even our silent protagonist), and a solid plot (it doesn't need to be Final Fantasy Tactics/7 proportions but there should be more to the game than the same beat 8 gyms, beat E4, roll credits).
4. Game breaking glitches and events: One particular hack for the anime (AshGray?) is very specific about the order of what you do and when. My first play through, I did an event wrong and I couldn't continue and this was in the beginning of the game. No game should be that specific and picky about how you play it to the point that you can't progress due to minor errors.