For me, its a. Spelling and Grammar. Please people, I advise typing EVERYTHING into MS Word, Pages, OpenOffice or whatever word processing program you have with spell check, and make sure it WORKS!!!! I've seen some pretty good games out there that have put me off because of spelling.
b. Very few new features. It's great to have a awesome game, you know? New storyline, new region, new cities, great everything... but it's basically the same features as every game has... I mean, what would it take to just have a nice event here or there that looks nice, hm hm? Maybe the Pokémon are all visible form a GUI at the top of the screen? That'd be cool. What about a fully interactive day/night system, with berries only growing in day and the Pokémon Center is closed at night? Cool! You get me?
c. Pokemon Essentials. Linking back to b, I know a lot of people use Pokemon Essentials and rely on it for a lot of things in their games. But there is little variety. Many people use default scripts, default settings, default resources, and just make a game from that. No creativity there whatsoever.