Final Fantasy XIII-2. My opinion.
- Most of the battle themes and the music
- Improved battle mechanics
- Plethora of sidequests
- Monster system* - it's like a customizeable third party member.
- Graphics are top-notch
- Neat interactive cutscenes and quick-time events
- Live trigger has some hilarious dialogue
- Characters are more likeable
- World feels more open, not "point A to point B" (although I didn't mind that in the first game)
- Forced to use the monster system (Where's my human party members like Lightning or even Snow or Hope?)
- Short main quest
- Unfocused storyline (it's all over the place)
- Lack of Sazh, Vanille and Fang
- DLC ending yet to be released
If you have about a half-hour to kill, watch this guy's opinion on FFXIII-2 (favorable for 13-2, but I don't totally agree with his opinion on FF13). Link