>>28676189The sequels have really good small tweaks and strong attention to detail both in gameplay and story following up from BW1. Going back to the first games is more difficult after enjoying all the little improvements in BW2.
You're better off going in the proper order as to avoid the sense of backwards progression by playing the sequels now and deciding to play the originals later. The first one won't take you very long (ie I'm at Victory Road as I write this and at the 23 hour mark with animations on more than off) so you could definitely play through both games before Sun and Moon even at a casual pace. Plus, you can link up the two games via DS download play for some extra story content in the sequels. It probably goes without saying, but make sure to stick with one color between the two games for a more consistent story (play White and White 2 or Black and Black 2.)
