I have to agree that BW's gameplay does tend to fall into a cycle, however almost every main series Pokemon game does. The only one that doesn't, in my opinion, is Pokemon Red Blue and Yellow, as the midgame is very open to whatever you want to do, and as you do things, more and more of the world opens up to you.
On another note, the elemental monkey has a fatal flaw: evolving too early. If you either aren't aware of how Stone evolutions work or don't have a guide book, you can EASILY miss out of Scald/Flame Burst/Seed Bomb on one of the Pan trio, as their stone is given to you RIGHT at the correct time to possibly screw you over. This easily cripples them, almost making them unusable at that point unless trained to insane heights, as they already have pretty meager defenses, even for singleplayer. The only salvagable one at that point is Simipour, which can learn Scald or Surf soon before/after the Ground Gym.