Okay, so I started a new game in Emerald the other day. I've just beaten Norman and am ready to head to the next location (Fortree, right?). And, just as I suspected, the game got very dull very suddenly; just after the fourth gym seems to be the point in the game that one can't keep his levels high enough just by facing the trainers that he meets along the way.
It's the point in the game that one has to start grinding excessively to keep up.
This is why I like RPGs like Paper Mario, where the battles were challenging, but not dependent on level.