Japanese Reviews For Final Fantasy Xiii-2

Same concept? Not really. Depends on what you meant by "concept".
Gameplay changed: In games like FF X-2 (on PS2) you could control all characters). FF XIII/XIII-2 (Xbox360) you can only control the "leader". Changing a character's "job" is harder in newer games, you can't change to whatever you want in mid-battle, unlike FF X-2 where you could easily press R1 (if I'm right) and decide which one to choose. In new ones you can only modify them via the menu. Never in mid-battle.
"Techniques" changed: Before the games were mostly concentrated on individual work, since you could change your job to whatever you want, and control each character. Now it's more up to teamwork, for strong opponents, you require having a strong SYN to put good defense. A strong SAB to put good curses, a good MED to cure quickly.
"Plot" changed: Well that happens in all games, it'll be boring if there's same plot all over again. But in the end they're all fighting for what they think is justice. Although they had the army against them in FF XIII.
Only thing that remained the same is the usage of the spirits (known as Eidolons in newer versions), however their names changed. Shiva and Ifrit were most common, however spirits like Odin, Alexander, and the others resurfaced, after not having that much fame. Some weapons' names have remained, and some skills like "Haste" and stuff like "Hastega", you know the suffix to show the importance of the skill, they only remained from older versions.