Well the first one is really difficult, but doesn't have much of a story......, the 2nd one though has a REALLY good plot if you pay attention to it and do a certain quest pertaining to it, and the 3rd one has a plot to do with ancient artifacts and the bad guys trying to become immortal by obtaining them.
Gameplay-wise, The 3rd one is the only Pokemon game that actually lets you skip the tutorials if you already know them.... only some that don't include new features though. The 2nd one you start out in a Ranger School and go through the life of a Pokemon Ranger, The Ranger School part is pretty boring but once you get past it, it gets way, way better, but you have to have the patience. For the 1st, I just say, skip it, because that was the time where Pokemon was just developing and testing things out for the DS, and keep in mind the game came out before Diamond and Pearl, so they weren't sure what to do with it.
I would recommend these games, but only if you have enough patience for a LOT of text (1st & 2nd), and Plot (2nd & 3rd).