wow, grassguy and Amp are out of their mind :P (no offense)!
i guess i experienced it like this:
R/B/Y: I saw some episodes of the anime, got fascinated by the cards and stuff and wanted to explore the world. huge adventure.
G/S/C: New pokemon, a cool new world with good stories (goldenrod is cool), many cool features like daycare and day/night and also a return to Kanto where all those famous character grew older, very cool.
R/S/E: Strange new world, nothing new, no connection to the previous games, the anime or whatever. Just more of the same.
D/P: Cool new world. Many new features. WiFi! But then again; i dont remember much of the single player part, since i played it in the week my girlfriend was at my place before she would travel the world for a long time and she was pissed when i played the game so i had to play it secretely without sound when she was asleep...
So.. They all have pros, except for R/S/E, that just really sucked.