first of all, I don't recall ONCE saying that I was a "pokemon fan".. I don't play for loyalty, or for pokemon, I play for the GAMEPLAY. I'll check it out, but if I'm not enthused within thirty seconds, I can safely say that as a standalone, it would never have succeeded
Not many people play Pokemon for the plot, or if they do, they aren't thinking about it all that hard. While many 6-11 year old kids might get a kick out of the 20 hour main game*, it's what you can do AFTER the main game is done with that keeps people turning on their GBA/DS for dozens of hours even though the credits have rolled.
There's the Battle Tower, which is basically "What if Gamefreak made an in-game competitive environment?".
There's Wi-Fi play, where you can play casually against friends, or in a competitive Smogon like environment with clauses and stuff.
Trading is only worth it if you have others to trade with, since the GTS won't help you with Pokemon you haven't already seen.
There's breeding, and for legends, soft resetting for good stats. This is very helpful if you want to get into trading but don't have anything to offer.
And all of these above topics focus on certain game mechanics (EVs, IVs, natures, abilities, etc).
Many more that I didn't list.
*The main games always have the same central plot with regional modifications. Different starters of the same general type, some type of Pokemon gang, the Plot-device/legendary Pokemon that are tired into regional myths, and your cocky rival.
You can also wait until March and just get Platinum. The plot will be extended/modified, more Pokemon will be available, and a few other nifty additions.