Strangely enough, my favorite Pokemon game is one that I've never owned, and that's Emerald (with HeartGold a close second). For the longest time, I would play through the games and once I finished with the main story, there wasn't a heck of a lot left to do. Emerald added the Battle Frontier, which added an entirely new dimension to the game. I enjoyed the Battle Pike the most, despite making it to the Brain dozens of times, but never being able to win. I hated when I had to give it back to my cousin, but I can honestly say I've never had more fun playing a Pokemon game.