The CoroCoro Magazine has been leaked, as seen on Bulbapedia.
The games take place in the Unova Region again, as expected.
In addition to that, the new protagonists seem to live in a new Starting Town: Hiougi City.
Since Pokémon Gold and Silver, this is the first time for Pokémon, to have a true sequel.
The only times that happened, were the switch from Pokémon Red and Blue to Pokémon Gold and Silver, and the switch from Pokémon Colosseum to Pokémon XD: Gales of Darkness.

The changes, known so far (direct Copy/Paste from Bulbapedia)
The first two pages reveal information about the changes to Unova and Black and White Kyurem:

• White Kyurem is 3.6m, 325 kg. Ice Burn is its signature move
• Black Kyurem is 3.3m, 325 kg. Freeze Shock is its signature move.
• The game is set 2 years after Pokémon Black and White.
• There have been many changes to the region. There appears to be an encroaching ice sheet or glacier, and the water in the area around the Entralink has dried up.
• 300 Pokémon in addition to the original 156 Unova Pokémon are now available.
• The Unova Pokédex also appears to have drastically changed, with Riolu being #033, Psyduck being #026, and Metagross being #264.
• The Pokémon Riolu, Psyduck, Metagross, Tyranitar, Eevee, Lapras, Arcanine, Weavile, and Mankey all appear to be in the new regional Unova Pokédex.

The next two pages reveal information about the new player characters, rival, and Gym Leaders:

• There are two new player characters; the male is the characters revealed yesterday on the cover, while the female has not been seen before.
• The character wearing red that was seen yesterday is the new rival; he is said to be a childhood friend of the player.
• The rival is quoted as saying “From now, I’m going to rage!”
• The girl with the guitar is Homika; a new Poison-type Gym Leader. Her Gym is said to be a “Live House” (a Japanese term for a music club where live bands play). She will appear in the anime in an episode on June 14.
• The tanned male in the swimming costume is Shizui; he’s a new Water-type Gym Leader.
• The man in the lab coat is Akuroma. He is researching Pokémon strength. A cut-off portion of the photo mentions he is doing something regarding the latent abilities of Pokémon.

The next two pages reveal information about the new starting city:

• The new starting city is Hiougi City, located in the south-west of the map.
• Its main point of interest is its lookout. There is a Pokemon Center and Trainers’ School; this is the first time your starting city has included either, as well as the first time the starting location is a city and not a town.

Scans (click them to enlarge)