I could write an entire review of the series about how godly it is but I'm fairly sure every self-respecting review will praise the game just as much.
I can't recommend it enough, really. What console are you getting this? The PSVITA version, The Golden? If it is, congrats, I've been meaning to get a Vita just for this game - which is the definitive version.
The series are a bit like Final Fantasy: entries aren't directly related and each has it's own story so P4 is as good as an entry point as any. If you still have a PS2 (haha) or own a PSP, get Persona 3 as well: IMO, the story is even stronger on the third (the PSP version has everything but the ultra-hard storyline that takes place after the main story, which was included on the PS2 FES version. On the plus side you can play the entire game as a female character, which warrants some differences on how the side-stories unfold).