The following list will contain spoilers
New Type (Fairy) and with it a New Eevee-lution! Dragons beware
The 2 new Anchients look awesome!
Totally changed up frontier!
Set in france! and There's no sprites!
able to ride pokemon (only a select few) roller skating, diagonal movement (avoid trainers)
3-d graphics (it could be a plus)
Able to change outfits! as well as groom and play with your pokemon
an "EV" or effor value training Gym (EV training is what sets pros and average players apart)
They also get more into the Contest side of Pokemon.
Horde Encounters (Moves like EarthQuake and swift will become a must)
Sky Battles! (Only flying and "levitate abilities allowed!) I wonder if you equip an Air Ballon to a pokemon it will be allowed in...
And Finally Mega-Evolutions!
I love Kangaskhan and Venasur's new abilities Parental bond and thick fat but Lucaio's Adaptability ,Blaziken's Speed boost,Garchomp's sand force and Mawile's Huge Power are definite game changers!
Kangaskhan's ability might be over powered with the right combos.
Venasaur has 4 weaknesses Psychic,Flying,Ice and Fire and with thick fat it removes Ice and fire from the list. So with a high special deffence He'll no doubt become an OU.
Lucario's adaptability is self explanitory
Blaziken for a long time has been thought to be the best Starter of any generation competitive wise with it's great move pool and attack stats but it's speed was it's only problem ..this ability will get it a spot in OU (Over used) in the Meta-Game.
Garchomp's Sand Force is gonna garentee's Sandstorm a spot in his moveset and will make his already Overpowered Stab boosted Earthquake that much more powerful. Plus Draco Metor or Dragon Rush with Garchomp's speed would almost instantly own any Flying type.. and ohh god with sword dance...He's OU.
And Mawile's Huge Power will probably get him used a lot more often.
and uhh I like Mega-Charizard Y's Drought ability. In a double battle with a Regular Venasaur (with clorophil ability) that has high SpDef and SpAttk Venasaur can basically rapid Fire Solarbeam. And still have great coverage with Charizard's way Boosted STAB Fire attacks to get full use of both abilities.
Also In the Anime/Manga Department!
Pokemon: The Origin ! has been subbed and it's pretty awesome following the story of Red (cause ash is a f*** up)
Also a shout out from the site SmackJeeves because they have two of my favorite fanfictions.
Mokepon is a pretty cool "manga-ish" styled pokemon fanfiction that has quite a bit of comedy and updates a page every week.
and A more "hand drawn" story of a trainer and her struggles. It's based on true events in her game as she takes on the "Nuzlocke" challenge.
Both are great and If you don't like them at first I ask that you at least read 2 chapters before you judge..trust me. If you don't know what the Nuzlocke challenge is go here http://www.nuzlocke.com/
It's basically if your pokemon faints it dies and you can only catch the first pokemon you see in each route. (Starting after you receive your first 5 pokeballs) An optional challenge is you have to name all of the pokemon you catch. (Adds to the attachment you're no doubt going to gain to your pokemon)
And here's a tip ,if you're not gonna get both games then get Pokemon X ..trust me
Charizard and Mewtwo's X mega evolution looks way cooler then their Y counterparts. Though I'd say "shiny" charizard Y looks cooler and the ability's better (for my way of playing) Though I plan on getting both games.