It has Wi-Fi, support, meaning that you can trade/battle with anyone anywhere provided they give you their friend code. Meaning, I could trade with you despite being on different continents.
It's also not an entirely new set, but I'm not sure if all of the Pokemon from the previous games in the series (meaning 500+) will be in the new games or if they'll just cherry-pick a certain number from Red/Blue, Gold/Silver, etc., and then add the new ones in to that set.
Also, they brought back the time system from Gold/Silver, meaning you'll find different types of Pokemon at different times of day. However, the time of day is also supposed to affect certain moves, meaning certain attacks will be more or less powerful at night, apparently.
That's all I know, except that the graphics are apparently greatly improved over the GBA games. Since I haven't played Pokemon since the Game Boy Color days, I'm sure it will look great from my perspective.