It was the first gen I skipped because I didn't have a Game Boy Advance, but mostly I loved the day-night cycle of Gold/Silver and it wasn't in the original version.
From what I've seen the world has wayyyy to much surfing so hopefully the balance the map a bit more. In a perfect world they'd kill off the HMs, but that won't happen.
3D in and out of battles, unlike in X/Y, would be nice. A return of the battle maison.
But really I just want to see what I missed out on all those years ago.