Wow, a see half the people in this thread complaining about people who use anything outside of what pokemon original created as bad... Then what's the point of hacking if you are just doing it exactly like every other pokemon game? Yeah, some people do it bad, but not everyone. D:
Then they want to talk about un-originality >.>
Anyways, for me what throws me off the most is bad grammar, people who try to hard to be 'clever' with there stuff, people who use BAD fakemon(not just badly sprited) people who don't use any fakemon. And people who try waaay to hard to be 'different' then pokemon. I do like to see some new stuff, but if it's just so far out there it doesn't even feel like pokemon any more, then I just won't enjoy playing it. Not that it's a bad hack, pokemon is about the only hand-held game I will play, and if it doesn't feel like pokemon gameplay wise, then it's not going to keep me interested.
I do have to say, you should only use fake-mon if they are a good bit above average in spriting. Decent ones, splices, and the like, (not to mention BAD ones) should not be put into the game. Also they need to have finally worked out typing, move sets, stats, evolution chains, and names, so they FEEL like real pokemon.
Really, everything just needs a balance of 'new enough to be worth playing' but 'not so new it's not pokemon anymore.'