Persona 4 has always been in my top 5 games of all time.
From a fan point of view, this game has more personas, mixes things up a little from the original game, more story which is always good, etc. Plus it was great to see some of my favourite characters on a portable console in HD.
From a technical point of view, the gameplay is a lot smoother than the original Persona 4, allowing for a more enjoyable experience. The game also has more difficulties, allowing for an even easier or more difficult game.
If you buy any one PlayStation Vita game, make sure it this. You will not be disappointed.