Fans of XIII will have a blast.
Thus far, I'm truly enjoying XIII-2. The combat system is just as fun with some new additions. The feral link can be thought of as the new limit break system and the cinematic events are timed well enough that even I can get the button presses in time.
The Historia Crux allows you to go back and forth to different times and areas. A system is also implemented that allows you to close a gate and then replay that area in order to achieve different outcomes.
I'm also enjoying the summon system where monsters can join your party. Hunting down various creatures that you want to have in your party is a simple way to level your characters and creatures. Although, as most Final Fantasy fans can tell you, wait on trying to tackle the Tonberry until you're leveled up.
I'm playing through on normal mode and like XIII, you need to maintain your paradigms in order to succeed in boss battles. Some bosses have taken several attempts in order to determine what paradigms work the best.
Many reviewers have said that this game will take 20-30 hrs for a play-through. For me, it's going to take a lot longer. I'm enjoying finding the various fragments scattered across the Historia Crux and plan to take my time reaching the end.