Far and away, the best Final Fantasy title of this generation, quite possibly the best RPG of this generation in general
The new battle system is the most significant change. Some of the extreme fanboys will feel out of place, but for most gamers, the new battle system is a breath of fresh air. It's not something that I would like to see in all FF games from this point forward, but it is still something that they could use every other, or every third title for a change of pace.
The licence system picks up where the bright spot of FFX (the sphere system) left off. It provides a great deal customizing options, and gives a good amount of replay value.
The sound is great, but the lack of Uematsu involvement is noticeable. But, I suppose that when you're used to Uematsu, nothing really has a chance of measuring up.
Final Fantasy XII is the best in the series since the fantastic FFIX (by no conicidence, the IX team worked on XII), and is definitely a top-5 in the series, though I do think that VI and IX are better. Overall, the only RPG of this generation that truely rivals it is Dragon Quest VIII.