You really should play red/yellow and silver to get in the "pokemon vibe". Also platinum, because that was a cool game, as it was diamond and pearl combined, and an added "world" which was pretty interesting. And soul silver is definately a game you want to play; even though it is a remake of silver, there are a lot of added features that are really enjoyable (the pokeathlon, the pokemon following you)
I think the 3rd generation of pokemon (ruby, sapphire, emerald) were the least impressive, and i get bored with them a lot quicker. (I also don't really dig the graphics style and music; but that's me)