The best part about this game in my opinion is the overall vas exploration and hidden secrets all over. I have always been the type to work hard to find all a game has to offer and FFXIII-2 has tons. Monster collection, which I originally thought was a terrible addition to fill in the spot of a third character, is so much fun and very addicting. Almost every monster you fight, you have a chance of collecting them in a crystal, having them join your party. Each one has a specific role and their own unique feral attacks. Overall, it's a fantastic addition to the game.
When you feel like taking a break from searching for Lightning, there is an amusement park style casino where you can play slots and raise chocobo's for the races to earn some nice prizes and gil. There are a few areas here that are not open yet. If you talk to an employee NPC, you will hear that these areas are under construction and will be available at a later date. Hinting that new games will be available through DLC, including a new card game next to the slots. Square Enix already has me itching for the DLC.
The graphics and gameplay mechanics are almost the same, just improved and move at a much faster rate than XIII. Although, the story does take a little while to get interesting and can be very confusing at times. Nothing is forced and you have the freedom to explore and grind to lvl 99 from the very beginning without even touching the main story line. (Although I would pace yourself on leveling too fast, because the fights will get super easy) No limitations or caps are put on you. The main story line may take about 25 hours to complete, but the amount of content meant to be explored will have you playing for at least 50-60 hours easily. Not to mention the DLC they plan on releasing later on. They really listened to the fanbase and have given us a product that is both fun and entertaining. If you want a game that will have you hooked from the very beginning, pick this one up.
P.S. I came across a Tonberry King today...got my butt kicked in like 30 seconds. He is a beast.