A time traveling story that expands on the story presented in Final Fantasy XIII and tries to right some mistakes
First things first, despite the huge marketing campain behind the game with Lightning, the actual gameplay with her is limited to a couple battles and interactive sequences at the beginning of the game. From there on, you'll meet Noel and Serah, the main (and only two) playable characters of the game.
-Freedom: One of the big points on Square Enix's promotion was the freedom of action and the ability to explore the living and breathing world of Pulse. While this is true, it's important to note that most maps aren't incredibly big (worth exceptions being the giant city of Academia, Archylte Steppe and Dying World).
-World: This time around, feels completely alive and cities/camps do give a feeling of being part of a living world where our characters are just part of it, rather than mere spectators (as it happened on the city of Palumpolum or Eden on XIII, to name a few places).
-Historia Crux: Think of it like your world map, from the Historia Crux you'll be able to travel to any portal you want any moment you want. And even better, if you go back to a place you've already visited, you'll be put right where you were when you went back to the Historia Crux, rather than from its portal (as long as you go back through the Pause menu), which will save you a lot of travel time on certain side quests.
-Story: While it might be a bit tricky at times to understand what's going on, Final Fantasy XIII-2 does a much better work to present the story to the player through the different missions and the main storyline. Unlike XIII, that had many revealing points of the plot stored in a datalog that not many would read. Caius is a villain to be remembered in the Final Fantasy series, right along with the likes of Kefka and Sephiroth (and even better to some than Sephiroth, to which I agree).
-Battle System: The Battle System hasn't changed much from Final Fantasy XIII. If anything, it might be a bit overwhelming to players new to the game, as, if Final Fantasy XIII was too slow on unlocking the different battle mechanics (paradigm shifting, eidolons, etc), Final Fantasy XIII-2 unlocks everything right from the beginning.
-Difficulty: If you're an experienced Final Fantasy player, most boss battles will be fairly easy (on normal mode), however, some of these bosses might be a tough challenger for newcomers. The set of final encounters is remarkedly challenging if the characters haven't been overleveled.
If you're a newcomer or you're having a hard time for whatever reason, easy mode allows you to tackle every fight in the game at a reduced difficulty, and you can switch it in-game if you want to turn it up (or down) at any particular moment.
-Side missions: Side missions aren't nothing new to the FF series. However, XIII-2 does introduce them right from the beginning and will let you tackle on optional content if you want to take some time away from the main story or to complete it post-game. Most of these missions add to the story of the game.
-Monster taming: FF XIII-2 introduces a brand new feature in the game, monster taming. Long story short: every time you defeat a monster, there's a chance it will become a crystal, which, in turn, allows you to summon that monster to your side to aid you in battle. It's, by all means, a customizable 3rd party member. Every monster has a default role (COM/RAV/SEN...) but can learn abilities from other monsters.
-Character progression: The Crystarium is back, but this time it's been simplified and made more customizable. If XIII had a predefined path for every character and for each role, XIII-2 brings you a single Crystarium for each character and monster. It's one of the defining points in character customization, particularly if you are of the min/maxing type. But fear not, if you're not into min/maxing, you won't have any problems beating the game either.
-Post-game content: Final Fantasy XIII-2 has plenty of post-game content, however, you might find that most of the content is of similar difficulty to the final boss, which means there's no real "super boss" in the game for which you need to do a massive jump in your progression.
-Replayability: Although the game doesn't feature a New Game+, every portal can be closed and restarted as if you were there for the first time. This will allow you to experience whatever part of the game you've loved, and will also give you access to the paradox endings, which require you to tackle certain encounters in a different way.
-Conversation choices: A new feature on Final Fantasy is the ability to pick a particular answer at certain points in the game (pretty much in the same way Mass Effect, Dragon Age, Fallout and other games do). However, they seem to be largely inconsequential and won't really affect the outcome of the game.
-Live Triggers: In some of the cinematic sequences you'll be able to interact. Although nothing negative happens if you fail to (and even in one particular place you're required to fail if you want to see an additional boss encounter), there's a reward for completing all the live triggers of a given sequence.
-Endings: The "canon ending" is surprising. Either you'll love it or you'll hate it, but if you didn't have enough with one, the game comes with 9 more alternate endings (8 paradox endings + the expanded normal ending once all 160 2fragments have been acquired).
-Colisseum: Here you'll encounter some challenging creatures, including Omega (that will kick your low level ass if you dare to go there before reaching end-game) and currently Lightning and Amodar. All of them are tamable and do provide a fun challenge for your end-game characters. Square Enix has promised they'll expand the list of encounters through DLC, so we can expect to see more familiar faces making a comeback here (for the love of god, please give me Auron, I'll be a happy camper).
-Conclusion: Final Fantasy XIII-2 delivers on its premise. It's a game that tries to redeem the JRPG genre by giving you more freedom, bringing back the feeling of a living world, and also trying to get closer to Western RPGs (which might not necessarily be a good thing).
-The pros:
-The story is better presented to the player
-Monster taming adds an interesting layer of customization.
-Side quests
-Character customization is great.
-Replayability
-Puzzles are back! And for the most part they're fun
The cons:
-Battles are still fun, but not as challenging as they were in XIII except for a few exceptions.
-Monster developing is frustrating as you're required to buy large amounts of materials to develop your monsters.
-Lack of true super-bosses
-You'll eventually hate the Hands of Time puzzles.
If you loved Final Fantasy XIII, you'll love XIII-2. If you disliked XIII because of its lack of freedom or lack of cities/NPCs, Final Fantasy XIII-2 will most likely fix it. If you disliked the battle system, sorry, most likely you won't like it either in XIII-2.