Don't be fooled by the overwhelming amount of haters on this page. They're outrageously mis-representing it and I feel obligated to give a proper opinion of it.
The game play is certainly a lot faster and more engaging from the get go. You recruit a 3rd party member through capturing monsters, and this adds a bit more dynamic to the battle system. There are EXTREMELY difficult boss battle in this. Some you can avoid and return to in new game +, but I found it enjoyable to take them on at the level I was at. Just don't take on Atlas at a low level, you will be sad.
The music is awesome. Not the best Final Fantasy music ever written, but it plays its' part well. There is truly breathtaking orchestral pieces, especially during the opening sequence and the final moments of the game. Most else is computerized symphonic stuff that gives the battles and exploration a nice vibe. Plus I really liked "New World", even if the lyrics were a bit nonsensical.
The dialogue is probably the best we've seen in a Final Fantasy game. It's to the point, they don't beat around the metaphorical bush like XIII did. Sure it doesn't have the same non-voiced magic the old FFs had but times are changing. The voice actors especially were fantastic, especially Noel and Serah's VAs. Caius and Lightning's VAs did a fantastic job with the over-the-top dramatic stuff they were given.
The time travelling system is neat. Every area is unique to one another, and there's always something to do. Whether it's fighting powerful monsters, doing mundane side quests or chocobo races in the sky.
Did you hate XIIIs linearity? Then you will be pleased, it's gone.
And the graphics are amazing, such is expected of Final Fantasy.
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The cons?
Well, the story doesn't make much sense until quite a ways in.. In fact, even then, it's still sort of weird. Although having played right to the ending, I can kind of see why.
Emotionally, the dynamic between the main cast doesn't pick up until around half way through. Which is fine, but I felt like the chemistry between Noel and Serah was very lacking for a lot of the journey. In fact, because the story isn't very easy to pick up on, progressing sort of felt a bit underwhelming until around half way through. Oh it's not linear, and the battle system is a blast.
But expect to be occupied by the gameplay for a while. At least until the emotional drama makes its' dynamic entry.
Also, the moogle is annoying. Holy fuck. Someone shoot it.
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So all in all. It's worth the money you pay for it, for the most part.
+battle system
+music
+graphics
+exploration
-story takes a while to make sense
-characters have little chemistry for the first 10-15 hours