I remember there was a thread compiling a bunch of this stuff. Man, X & Y, to me were games that could've been really awesome, but there was a ton of wasted potential there. Kalos was really neat (though I think they could've tweaked Lumiose so it wasn't a clusterfuck), the music was based, and there was a lot of neat ideas that just felt rushed.
Here's a couple yet to get mentioned:
-Az's Floette
-Couriway railway
-Mysterious message in the train station/ person waiting (or was this one solved?)
Do you all remember the statues in the garden threads that went up around XY's release, too?