oh i personally think they were good until about ruby and sapphire :| never really cared for the ones after that
I'm going to maintain that when they hit Ruby and Sapphire that they'd perfected the series and were out of good ideas for Pokemon. I maintain this, because after Ruby era the games are essentially a copy paste of the last one, with more and more ridiculous outfits for the protagonists and that same secret braille language and loads and loads of legendaries that effect the forces of the entire planet. It really spiralled out of control, me thinks.
Especially when you look at its humble origins. I'm sure wikipedia has this somewhere, but it started off as Satoshi whatever his name is wanting to make a game related to Bug Catching, which was one of his favorite childhood hobbies. From Bug Catching to God Subduing. Hmmm.