Yoshinori Kitase and Motomu Toriyama, the Producer and Director from FFXIII-2 have revealed some new information about the game, which had been pretty vague until this point.

Lightning is the story's backbone, she will appear in the game at some point and become playable
Final Fantasy XIII-2 will be story driven, but players can actively trigger side quests and events, explore new areas as the story progresses. There will be many choices for the players
New character Noel will have very different personality from Snow, but his background cannot be revealed yet
A new feature added to the battle system to allow you to capture monsters and use them in battle. You can assign paradigm to monsters and group them together in different ways. Each type of monster has specific roles
Players can start playing FFXIII-2 without knowing the story in FFXIII
You can continue to play the game after the main story is completed. The team is looking to offer player a different form of repeat play
FFXIII-2 will have multiple endings, it is a first in the main series. Unlike FFX-2, FFXIII-2 is a direct sequel to FFXIII, not a side story / gaiden like FFX-2. Since both XIII and XIII-2 share similar world setting and battle system, the team would want to offer new elements in the gameplay area.
In the E3 trailer you can find Lightning battles against Chaos Bahamut with her Odin summon. Toriyama said there are multiple Bahamuts, the Chaos Bahamut is a slightly different existence from a summon.
Serah does not have her own summon, instead she can summon monsters to join her in battles
You can find hidden / secret side quests and missions by speaking with certain NPC, or choosing different options when you speak to them
Mog is Serah's friend, he can help the team uncover hidden treasures, and he can also transform into bow and arrow or sword
Players can jump freely in the field, you can reach hidden treasure and hidden paths
Noel's two weapons can combine into a spear
Another new character called Alyssa will be playable, she is the character with blonde hair
The image poster with both Lightning and Serah is a surrealism poster reflecting the darker story in FFXIII-2
Development of the game is very smooth, the game shouldn't be delayed in Japan
It is just pieces, but the source looks to be Japanese, so I'm guessing that they were just translating and phrasing things as best as they could. But it does certainly start painting a new and interesting picture for what is the sequel of FFXIII, game that has been very polarizing for people.

I guess an interesting note is that they consider FFX-2 a sequel, but a Gaiden, a side story. Which considering the story told, I guess that would be a fair point. But the general public and the way that they marketed it to us made us think sequel. Interesting, which is funny because FFX-2 did have multiple endings.