I've been out of the game a while, and could use some help catching back up

I've been away from pokemon since about Gold/Silver, and all the new talk about X/Y has me really pumped up to jump back in. The only thing is, I feel light-years away (light-years measures distance, not time, mind you) from being prepared for such a Pokemon journey. Can you guys fill me in a little on what I've missed and the game challenges I should go through to be prepared to catch 'em all?