I don't really do the (main game title here)+ games. I don't need 700+ pokemon in gens 1 and 2, nor do I need it to be a grindfest. I enjoy fakemon, when they're well made and there's enough to build a team with them.
For me I'd have to say the deal-breaker is, gimme a new region. Aside from Red Adventures, Ash Gray, and Sirius / Altair, I basically refuse to play Kanto or Hoenn.
I expect smarter trainer AI, as stated earlier in the thread "no need to use leer on me 4 times" lmao. I don't mind losing battles, but I shouldn't have to spend an hour speed grinding to beat a non-boss-type trainer. Trainer pokemon variety is also important, make me use a balanced team and not a team carrier.
Give me unconventional starters. I love using different mon's in different games. Pokemon that often go overlooked in a regular game. Like, please do not just put Pidgey, Rattata and Nidoran on the first route and so on. Make me really think about who I want on my team, and for what reasons.
Postgame is important to me, I don't wanna just collect 8 badges, beat the league, and call it a day. So some form of story other than "you're the champion, go do the thing" is appreciated.
I loathe NPC's who say useless things like "the pc in the corner is free to use". Like yeah, I'm well aware my dude. Also 2009 "edgy" humor is seriously outdated. LOLSORANDOMXD humor is also, seriously outdated. I'll probably never play CAWPS or Outlaw.
Could honestly care less if there's the stat split everyone's always so concerned about (although it's basically normal now). I care more about exploring and story, and building a team with good type coverage than I care about stats.
Custom events! For example lots of gen 2 hacks just retext the events in order, and it's very obvious.
A lower shiny rate is nice but not mandatory. Running shoes early on is nice but not mandatory.
Just nitpicky things from there so I'll leave it at that.